Document missing server config options

[MadLittleMods]

I was looking into the USE_FROZEN_DICTS option during the review of #18103 (comment) and noticed that there are several other server config options that aren't in the docs.

Dev notes

synapse/synapse/config/server.py

Lines 421 to 424 in a9361c4

	self.daemonize = bool(config.get("daemonize"))
	self.print_pidfile = bool(config.get("print_pidfile"))
	self.user_agent_suffix = config.get("user_agent_suffix")
	self.use_frozen_dicts = config.get("use_frozen_dicts", False)

synapse/synapse/config/server.py

Line 774 in a9361c4

manhole = config.get("manhole")

Pull Request Checklist

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• Pull request includes a changelog file. The entry should:
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• Code style is correct
  (run the linters)

[MadLittleMods]

Thanks for the review @erikjohnston 🦡