Add Chronyd Sync Module

Support for operating alongside the chronyd service is now provided in a separate crny sync module. For example:

[general]
sync_module crny crny1

To aid the transition from existing behavior under the NTP sync module, sfptpd implicitly creates a suitable instance of the crny sync module. To disable this for simplified logging and diagnostics, specify a crny sync module with no instances:

[general]
sync_module crny

See the sync_module option in Configuration Options, Chronyd Sync Module, and Chronyd.