fix: Enable the same atSign to be used on both sides (client and server) of an AtRpc interaction

[gkc]

- What I did
Main thing:

• fix: Enable the same atSign to be used on both sides (client and server) of an AtRpc interaction

- How I did it

• Added optional parameters isClient and isServer to AtRpc constructor. If isServer is set, then the AtRpc will listen to the requests regex. If isClient is set, then the AtRpc will listen to the responses regex.

- Other things of note:

• fix: LocalSecondary.isEnrollmentAuthorizedForOperation now checks if the key in question is a local key, in which case the answer is always yes.
• fix: AtClientImpl._putInternal now also checks if the key in question is a local key, in which case it does not require that the key have a namespace

- Chores etc

• fix: changed severity of a log message in SyncServiceImpl from severe to warning, because sync failures can happen for a whole bunch of mundane reasons.
• test: Moved test setup code in sync_service_test.dart into a setUp() method where it belongs. As a result, found a missing when in one of the tests, fixed that
• docs: moved a @deprecated annotation to the place dart format prefers it to be
• chore: tightened up logging in SyncServiceImpl

- How to verify it
Tests pass