Changes

• Add support for GCM initialization - move initialize encryption and initalize decryption processes to a separate functions. GCM initialization takes more steps, the IV len is being set separately.
• extract padding configuration to a separate function
• add finalize(out, tag) method to finalize the GCM encryption or decryption. For encryption the finalize method returns the generated tag while for decryption the tag is being validated
• add ERROR logs before throws in cases where something went wrong
• add AAD option for GCM initialization

Testing

• unit tests for both existing CBC and GCM mode

Next steps: enabling GCM once it's available in backend

1. switch CipherContext mode to GCM
2. switch finalize method to finalize(out, tag)
3. update metadata in cloud clients
4. test the solution e2e