mod_turncredentials: Add 'transport' attribute XEP-0215 recommends using 'transport' attribute and since coturn can work in both TCP and UPD modes this patch adds one <service> element for each combination of STUN/TURN and TCP/UDP.

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summary: Log a message once per minute
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This module sends `-- MARK --` to the log once per minute. This may be
useful to give a sense of how busy the server is or see that logging and
timers are still working.