Add support to transport syslogs over TLS. Since TLS params essentially
require passing host and port separately, add a boolean flag to the
configuration template and also use the same `action` format for
plaintext logs. This allows seamless transition.
The plaintext host:port is picked from `AUDIT_LOGGING_ENDPOINT` (as
earlier) and from `AUDIT_LOGGING_TLS_ENDPOINT`. The TLS host:port is
used when defined and non-empty.
`remote_endpoint` is split separately to hostname and port as required
by `omfwd` module.
Also the address parsing and config content generation are split to more
testable functions with basic tests added.