feat: Complete keystream implementation

[XavierChanth]

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

Right now keystream uses notify instead of sync, which means it does not work for self keys.

Describe the solution you'd like

~~Finish my previous work on https://github.com/atsign-foundation/at_client_sdk/pull/803 now that it is no longer block by sync enhancements.~~

Implement auto-notifications for self keys, until sync is near real-time.

Describe alternatives you've considered

No response

Additional context

No response

[gkc]

Current sync is not near-real-time, but notify is. In the interests of app user experience can I suggest we resolve this for now by implementing auto-notifications for self keys, and move to using sync when sync becomes near-real-time

[XavierChanth]

To be discussed further