Ingest Zendesk knowledge base articles

[shillion]

Please describe the feature you'd like to see
Jake Witz is working on publishing our Zendesk knowledge base articles to the public. We should ingest these in Ask Astro.

Acceptance Criteria

• All checks and tests in the CI should pass
• Integration tests — add some queries to our test set that are related to this source
• Add Zendesk to the documentation as a source

[jwitz]

Requirements for this project:

• Ask Astro should ONLY pull articles designated as visible to "Signed-in users". We have internal content for CRE only that won't be beneficial or relevant to customer asks.
• Zendesk articles are designed to be atomic, and compounding them together in a single response might be less effective than for other content. Ask Astro responses should reflect this

Extras:

• Zendesk articles have a lot of metadata tags that make could be used to help Ask Astro filter and navigate articles, we should take advantage of this if possible.