DOC-12091: Add Analytics reference to Capella

[simon-dew]

Docs issue: DOC-12091

This PR adds the Analytics reference guide to the Capella operational documentation. For historical reasons, the Analytics developer documentation is in its own repo, docs-analytics. This PR adds the capella branch of that repo to the build.

This effort was timeboxed, and I ran out of time to complete it, so parking my progress here.

Docs preview: Analyze Large Datasets Credentials: Preview docs for internal review

This can't be merged until the following linked PRs are ready:

• https://github.com/couchbase/docs-capella/pull/107
• https://github.com/couchbase/docs-analytics/pull/45