feat: Generate admin command documentation

The first part of getting admin command docs on the website.

Next is is including it in the same way we do the example config or
readme.

There's also the beginnings of manpage generation here, although it's
kinda sus and I'm not sure how it's supposed to work. I'll leave that to
anyone who wants to package it.

We introduce the beginings of the xtask pattern here - we do a lot of
file generation, I thought it would be best to avoid doing that on every
compilation. It also helps avoid lots of runtime deps.

We'll need to document generating this stuff & probably add pre-commit
hooks for it, though.

conduwuit-example.toml

@@ -662,12 +662,18 @@
 
 # Enable journald logging on Unix platforms
 #
+# When enabled, log output will be sent to the systemd journal
+# This is only supported on Unix platforms
+#
 #log_to_journald = false
 
 # The syslog identifier to use with journald logging
+#
 # Only used when journald logging is enabled
 #
-#journald_identifier = "conduwuit"
+# Defaults to the binary name
+#
+#journald_identifier =
 
 # OpenID token expiration/TTL in seconds.
 #