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.

Cargo.lock

@@ -1305,6 +1305,7 @@ dependencies = [
  "fail",
  "flate2",
  "futures",
+ "hostname-validator",
  "http 1.1.0",
  "indexmap 2.9.0",
  "itertools 0.10.5",
@@ -2771,6 +2772,12 @@ dependencies = [
  "windows",
 ]
 
+[[package]]
+name = "hostname-validator"
+version = "1.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f558a64ac9af88b5ba400d99b579451af0d39c6d360980045b91aac966d705e2"
+
 [[package]]
 name = "http"
 version = "0.2.9"