net/chrony: configuration overrides via confdir and sourcedir - #5639

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Describe the problem

there are some options for Chrony not available in the UI

Describe the proposed solution

this adds both confdir and sourcedir entries to chrony.conf for both /usr/local/etc/chrony/ and /var/run/chrony/.
the reason for both is that the man page for chrony.conf gives the sourcedir example /var/run/chrony-dhcp which made me think it would be good to have both in case the user wants to make automation that uses volatile storage to avoid potential issues on power loss