mosquitto: support more config options in UCI

mosquitto: support more config options in UCI

Added many more UCI config options, particularly for bridge connections

The recently introduced username/password options for bridges are kept,
even though they have been deprecated upstream for a while.  In keeping
with this, while support is kept in UCI, the generated mosquitto.conf
file will always generate the "modern" remote_username/remote_password
options preferred by mosquitto instead.

Likewise for bridge clientid and remote_clientid options.

Signed-off-by: Karl Palsson <karlp@etactica.com>