dnsmasq: add handling of `dns-rr` to init script (add arbitrary resource records)

dnsmasq: add handling of `dns-rr` to init script (add arbitrary resource records)

Add support for handling of DNS RR (Resource Records) requests, which
are needed for the HTTPS Type 65 records, introduced to support the
DNS-based Service Discovery (DNS-SD) mechanism for HTTPS services and
defined in the RFC 9460 (9.1. Query Names for HTTPS RRs).

Ref: https://forum.openwrt.org/t/resolving-query-type-65-to-local-address-for-ios-clients-in-dnsmasq/179504/11

uci config usage:

config dnsrr
    option rrname 'foo.example.com'
    option rrnumber '65'
    option hexdata '00'

hexdata is optional.

Available since dnsmasq 2.62 (for around 12 years at this point).

Note: dnsmasq dns-rr are not affected by filter-rr

Tested on 22.03.5

Signed-off-by: Paul Donald <newtwen+github@gmail.com>
Tested-by: Vladimir Kochkovski <ask@getvladimir.com>
Link: https://github.com/openwrt/openwrt/pull/14975
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>