Update Couchbase Integration

[chedim]

Short description

The Alpakka Couchbase integration has not been updated in quite a while and is stated to reach the EOL. It would be nice if someone stepped up to update it instead :)

Details

I am a Couchbase employee and have been working on the update. I still need to add some more of new tests, but wanted to create this issue for submitting a draft PR for potential suggestions and recommendations by devs.

Thank you!