Add Couchbase VectorDB Support for AG2

[lokesh-couchbase]

This PR adds Couchbase Vector DB Support for AG2. Couchbase Vector Database has been part of Autogen 0.2 and we would like it to be part of AG2 package as well.

Please let us know if any other details are required from our end

Checks

• I've included any doc changes needed for https://ag2ai.github.io/ag2/. See https://ag2ai.github.io/ag2/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[marklysze]

Thanks @lokesh-couchbase, a solid PR! Are you on Discord? If so, would you be able to reach out to me, msze_, so we can got a CLA over to you?

[marklysze]

Hey @lokesh-couchbase, I'm working through testing it and I'll add some comments. As it follows the other vector DB examples it aligns well with what's needed, so thanks for doing that.

I am having an issue connecting with my Couchbase Capella using the connection string, storing it in the environment variable CB_CONN_STR. I'll send my connecting string to you in Discord.

[marklysze]

@lokesh-couchbase, thanks again for the PR - as it requires the setup of a number of things within the Couchbase Capella Web Console, I think we need to provide, at least, a bullet point list of things they need to do.

At the moment the line in the notebook should be expanded with more guidance:
"Ensure you have a Couchbase Capella cluster running. Read more on how to get started here"