ability for sync verb handler to skip delete commit entries to be sent to client

[murali-shris]

Is your feature request related to a problem? Please describe.

#2066
"Excessive Syncing of Deleted Keys: New clients must sync all keys, including numerous deletions, leading to significant time and space inefficiencies."

Describe the solution you'd like

• introduce a flag skipDeletes in sync verb handler.
• do not send keys that were eventually deleted in the sync list to client

Describe alternatives you've considered

No response

Additional context

No response

[murali-shris]

Complete some of the changes on server to skip delete entries.
While writing tests encountered a bug in _acceptKey in commit log keystore.
#2115
Will fix the bug and then resume work on this feature

[murali-shris]

Server changes:
#2097
Client changes:
https://github.com/atsign-foundation/at_client_sdk/tree/sync_skip_deletes
End2End testing in progress.Once successful, will run performance tests.
Server PR to be merged first once performance results are good

[murali-shris]

Implemented skipUntil changes and extensive unit tests on server
#2131
Changes in at_client in progress