nginx-util: fix deprecated openssl 3.0 functions

nginx-util: fix deprecated openssl 3.0 functions

Since upstream openwrt has been using openssl 3.0 for quite some time,
figured we could clean up some of the legacy code.

This PR updates the code for EC/RSA key generation.

nginx-util currently only generates 'ecc' keys, even though the
framework is there for rsa as well.

In order properly test the changes, I created two binaries:

'nginx-util-ssl'     (generates ec keys)
'nginx-util-ssl-rsa' (generates rsa keys)

where I would change line:455 in `src/nginx-ssl-util.hpp`

`auto pkey = gen_eckey(NID_secp384r1)` to `auto pkey = gen_rsakey(2048)`

Example with UCI config

```
config server '_rsa'
	list listen '443 ssl default_server'
	list listen '[::]:443 ssl default_server'
	option server_name '_rsa'
	list include 'restrict_locally'
	list include 'conf.d/*.locations'
	option uci_manage_ssl 'self-signed'
	option key_type 'rsa'
	option ssl_certificate '/etc/nginx/conf.d/_rsa.crt'
	option ssl_certificate_key '/etc/nginx/conf.d/_rsa.key'
	option ssl_session_cache 'shared:SSL:32k'
	option ssl_session_timeout '64m'
	option access_log 'off; # logd openwrt'
```

➤ /opt/bin/nginx-ssl-util-rsa add_ssl _rsa
Adding SSL directives to UCI server: nginx._rsa
	uci_manage_ssl='self-signed'
Created self-signed SSL certificate '/etc/nginx/conf.d/_rsa.crt' with key '/etc/nginx/conf.d/_rsa.key'.

[04/14/24 18:37:15](K-6.6.27)
root@WRX36 ~
➤ openssl x509 -in /etc/nginx/conf.d/_rsa.crt -text -noout
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            6d:55:a6:cd:52:25:31:fd:3c:78:66:24:82:5f:bb:b6:a6:fe:8f:c7
        Signature Algorithm: sha256WithRSAEncryption
        Issuer: C = ZZ, ST = Somewhere, L = None, CN = OpenWrt, O = OpenWrtBF399B64ACF71BC3
        Validity
            Not Before: Apr 14 22:37:15 2024 GMT
            Not After : Jul 16 22:37:15 2027 GMT
        Subject: C = ZZ, ST = Somewhere, L = None, CN = OpenWrt, O = OpenWrtBF399B64ACF71BC3
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:ac:52:71:af:25:e9:05:0a:a5:d7:86:d3:8d:0b:
                    66:e0:09:cf:2a:cd:a1:63:57:36:46:61:04:16:fe:
                    94:84:d0:20:ab:01:15:55:aa:a1:89:c2:85:a9:84:
                    47:ba:84:d7:1f:a9:0c:c0:f0:67:2f:81:1d:1b:3b:
                    31:d5:94:6e:a0:f0:e6:ec:26:91:4a:e2:fd:58:4c:
                    ac:b5:9e:a1:cd:7d:91:51:29:81:1d:3e:4a:d9:d1:
                    d5:f1:2f:34:2f:ca:95:dc:42:d5:c4:d3:d6:b2:91:
                    d5:19:61:a2:b5:b1:90:f0:83:88:ef:92:c9:bf:a4:
                    59:a9:d6:00:6f:1c:0d:70:16:40:cc:cb:c0:de:c4:
                    8f:00:83:a3:2f:77:ca:18:cd:7b:d4:77:96:47:78:
                    1b:c1:ff:08:86:93:79:91:8f:a7:95:71:46:06:69:
                    fc:cc:65:64:e7:99:11:cc:82:bb:39:6b:12:27:73:
                    0e:d1:e7:65:51:9e:ad:dc:b3:ff:3f:ba:b0:72:4f:
                    22:ad:7e:41:bb:3c:c7:80:30:81:5f:8b:32:f4:7f:
                    22:48:3f:3d:a9:eb:28:27:12:db:a9:63:c9:7e:e2:
                    ed:36:de:e7:68:31:4e:9c:c0:36:e8:f2:d9:3f:50:
                    09:50:a3:e8:7a:03:00:4f:8d:e1:10:eb:a1:87:44:
                    be:23
                Exponent: 65537 (0x10001)
    Signature Algorithm: sha256WithRSAEncryption
    Signature Value:
        06:7d:84:00:ac:8f:8b:a6:b6:b7:b5:ed:ee:7f:61:76:6d:ee:
        11:53:f6:d1:f8:95:ad:6c:d7:d0:3e:01:ac:bb:d7:7a:8d:59:
        80:ec:ba:b2:7b:78:5c:4f:5e:3f:f1:74:ad:d9:8c:a2:6b:08:
        9c:bf:b1:42:fd:8d:a6:35:48:4d:a7:2d:92:c9:45:66:77:32:
        a4:e0:ea:eb:e0:4a:42:f5:dd:ea:a2:c0:0a:66:5a:32:03:1d:
        e7:87:3a:7f:1e:00:ed:d0:21:01:d5:f9:e2:b1:e6:b7:cb:1c:
        67:11:de:69:7f:a2:ce:d0:fc:2d:f2:6c:33:84:4c:3d:f4:f6:
        60:6b:2e:31:b7:0c:41:2c:73:31:7e:94:19:a2:2b:6a:56:3f:
        07:37:71:97:28:58:91:63:b2:58:97:b2:aa:1e:d5:d9:6d:af:
        6f:a0:02:e0:06:39:b0:c9:f5:50:41:b5:58:41:6a:30:72:89:
        9a:67:7e:a1:7a:a5:02:b9:2a:f3:f8:93:4f:59:6e:b1:27:54:
        86:d1:ec:96:7a:dd:d1:44:6b:1e:3b:17:cf:15:64:ad:83:6b:
        63:20:2d:42:c3:28:68:14:de:12:4e:8a:c3:f3:10:c8:4b:4f:
        c7:d8:2b:a8:45:fb:3a:bd:9d:bd:08:71:08:09:ed:ea:9b:b9:
        3b:33:a6:a6

[04/14/24 18:37:27](K-6.6.27)
root@WRX36 ~
➤ /opt/bin/nginx-ssl-util add_ssl _ec
Adding SSL directives to UCI server: nginx._ec
	uci_manage_ssl='self-signed'
Created self-signed SSL certificate '/etc/nginx/conf.d/_ec.crt' with key '/etc/nginx/conf.d/_ec.key'.

[04/14/24 18:37:43](K-6.6.27)
root@WRX36 ~
➤ openssl x509 -in /etc/nginx/conf.d/_ec.crt -text -noout
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            55:32:fe:07:09:79:d1:40:d7:43:2e:45:3d:98:4a:77:65:d0:29:41
        Signature Algorithm: ecdsa-with-SHA256
        Issuer: C = ZZ, ST = Somewhere, L = None, CN = OpenWrt, O = OpenWrt2EDD40F41960C8C1
        Validity
            Not Before: Apr 14 22:37:43 2024 GMT
            Not After : Jul 16 22:37:43 2027 GMT
        Subject: C = ZZ, ST = Somewhere, L = None, CN = OpenWrt, O = OpenWrt2EDD40F41960C8C1
        Subject Public Key Info:
            Public Key Algorithm: id-ecPublicKey
                Public-Key: (384 bit)
                pub:
                    04:97:d2:b2:f0:c9:60:60:89:7e:ea:6f:48:1c:90:
                    8e:6d:1d:d8:58:46:8c:de:e9:50:e2:74:ea:d8:dd:
                    8c:d9:ed:f4:4c:b7:41:95:55:98:38:5a:9e:66:83:
                    b9:7c:79:71:9b:ec:18:ed:d9:09:3c:f7:64:32:ae:
                    59:ad:92:de:d7:c4:15:2e:e5:89:65:f4:29:8a:62:
                    a0:85:21:95:22:3a:38:e3:11:e6:f2:01:f6:50:62:
                    01:ed:68:0d:d0:0c:d4
                ASN1 OID: secp384r1
                NIST CURVE: P-384
    Signature Algorithm: ecdsa-with-SHA256
    Signature Value:
        30:65:02:30:78:af:d1:4f:57:b1:97:2b:87:aa:7f:a2:26:39:
        19:30:5c:4f:9c:f0:d7:ee:24:8e:a2:39:ec:70:af:16:eb:a6:
        72:96:d4:a7:2f:c1:38:f4:65:ed:ed:bf:22:c6:a4:6d:02:31:
        00:bc:ec:19:0e:3d:6a:d1:5a:ae:6d:5c:a3:ec:96:60:32:f9:
        6a:88:06:92:ed:c1:a7:44:2c:33:7a:22:72:0f:2a:ce:83:f0:
        f2:04:9e:49:60:ef:83:b4:7f:8b:af:61:c9

```

Maintainer: Peter Stadler <peter.stadler@student.uibk.ac.at>
Compile tested: aarch64, qualcommax, Master Branch
Run tested: aarch64, Dynalink DL-WRX36, Master Branch

Signed-off-by: Sean Khan <datapronix@protonmail.com>