account: Split user defined and volatile account parameters getters (2/2)

Use the new volatileAccountDetailsChanged as a replacement for
sipRegistrationStateChanged.

What this commit does *NOT* do:
 * Clean outdated SIP error messages
 * Forward TLS error messages
 * Forward other transport errors
 * Compute downtime timestamp

Those features will be part of future commits.

Refs #56143

Change-Id: I336cc6826b468a96e14ef08748c6718823bd647b