Support audit syslog over TLS (#12124)

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.

compute/compute-node.Dockerfile

@@ -1983,7 +1983,7 @@ RUN apt update && \
         locales \
         lsof \
         procps \
-        rsyslog \
+        rsyslog-gnutls \
         screen \
         tcpdump \
         $VERSION_INSTALLS && \