DOC-5600 Bring Pulsar connector docs to Astra Streaming

[aimurphy]

These pages are mostly the same for both Luna Streaming and Astra Streaming, so a lot of the content is now in docs-common. I didn't convert some small paragraphs to partials, but I converted a lot of the content to partials.

I couldn't share them 100% because Luna Streaming doesn't have the same connectors in every version, and Luna Streaming leans heavily on the Pulsar CLIs and doesn't use the REST API (at least not with curl). I am sure it's still possible, but I didn't want to introduce a new paradigm on these reference pages. Therefore, there are a few partials that live in the Astra Streaming & Luna Streaming repos.

• Astra Streaming and Luna Streaming each have their own versions of the following:
  • ROOT/partials/sinks/get-started.adoc
  • ROOT/partials/sinks/edit.adoc
  • ROOT/partials/sources/get-started.adoc
  • ROOT/partials/sources/edit.adoc
  • connectors/pages/index.adoc
• Astra Streaming and Luna Streaming each have pages for the sink and source connectors that pull partials from docs-common or locally.
• Removed all remaining links to streaming-learning
• Specific to Astra Streaming: Remove unnecessary astra-streaming: from xrefs.
• Specific to Astra Streaming: Move some API and CLI examples to the API and CLI reference-esque pages.

[plpesvc-ds]

Build successful! ✅
Pull requests with matching branch name doc-5600 included in the build:

• DOC-5600 Bring Pulsar connector docs to Astra Streaming #164 (this pull request)
• https://github.com/riptano/docs-common/pull/264
• DOC-5600 Pulsar connector pages pulsar-docs#185

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[mendonk]

LGTM