[Request]: Add gemini to list of supported connectors for Observability AI assistant

[dedemorton]

Description

We need to add the gemini connector to the list of supported connectors here.

We also need to align our docs better with other solutions (like security) that provide similar functionality. But for this issue, let's just get the connector and any config details added to our existing page.

Resources

This feature was implemented in elastic/kibana#188002

Which documentation set does this change impact?

Stateful and Serverless

Feature differences

No differences

What release is this request related to?

8.15

Collaboration model

The documentation team

Point of contact.

Main contact: @grabowskit

Stakeholders: n/a

[dedemorton]

This is mostly implemented in #4143 (just needs to be finalized and merged).

[dedemorton]

Closed by #4143