feat: add support for populating and using sharedKeyEnc

[akafredperry]

closes #367

- What I did

• Updated Java SDK to support shared encryption keys in the metadata (removing the need for sharedWith atSign to perform lookup to get the shared key, although that feature is retained as a fallback)
• Expanded tests for EncryptionUtils
• Added support for client config which set the SDK version and platform for the session
• Added support for JSON formatted error messages
• Minor usability feature for setting AtKeys

- How I did it

• Updated Metadata to include all the fields that are currently supported by the server
• Fixed bug in update params marshalling code (sharedKeyEnc was out of order)
• Enhanced SharedKeyCommands and Notifications to support sharedKeyEnc (and pubKeyhash, pubKeyCS)
• Added ClientConfig map to AuthenticatorCommands - client version will be populated from maven artifact version, clientId is UUID, platform is Java

- How to verify it

• Unit and Integration tests have been expanded to cover all the changes (these run as part of this pipeline) - coverage threshold has been increased to 80%
• Have tested put/get from Dart CLI and Java SDK

- Description for the changelog

support shared encryption keys in the metadata

[gkc]

LGTM thanks @akafredperry I think a good next step would be to implement at_talk in Java to verify interop of all of the core functionality