at_java: Bring Java client up to date with Dart client

[gkc]

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

Java client is lagging significantly behind Dart client in multiple ways

• APKAM
• Shared key exchange
• Encryption / decryption
• Notifications
• Logging

Describe the solution you'd like

Java AtClient needs feature parity with dart Client (apart from sync which should remain out of scope for Java client for now)

Describe alternatives you've considered

No response

Additional context

No response

[gkc]

Assigning myself, and allocating 4SP for PR75, this will probably take three sprints at 4SP per sprint