Doc: Add integration docs for Estuary Flow

[danthelion]

Motivation

This PR adds the integration guide to the docs page for Estuary Flow as discussed with @morsapaes.

Checklist

• [ ] This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• [ ] This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• [ ] If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• [ ] If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• [ ] This PR includes the following user-facing behavior changes:

[CLAassistant]

All committers have signed the CLA.

[danthelion]

Hey @morsapaes! I was wondering if there's anything I can add to this docs page to push it through the finish line

[morsapaes]

Hey, @danthelion! Sorry for the lag, we have a big backlog for documentation. I'll incorporate this into the updates we're making to the CDC documentation.