Docs/igw docs day refactor

[trujillo-adam]

Description

This PR refactors the existing ingress gateway documentation into overview, usage, and configuration reference content types. We edited some content for clarity and so that it fit into the content type paradigm, but it is mostly unchanged. Please review for accuracy.

Preview pages:

• Overview
• Main usage page
• Secondary usage page: For this page, please verify the order of the steps. It follows the order of the existing page, but a few questions emerged as we created the draft. Additionally, please verify the description under the 'Configure static SDS clusters' step.
• Configuration reference

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

[im2nguyen]

Looks good, a couple small nits, but pre-approving so you're not blocked from merging

I noticed you used <CodeBlock> instead of <CodeBlockConfig>, can you please change this before merging? Also, this is a nit, but newlines are inconsistent after headings and codefences, would be nice if we can be consistent with a single new line after each one

[im2nguyen]

Looks good, a couple small nits, but pre-approving so you're not blocked from merging

I noticed you used <CodeBlock> instead of <CodeBlockConfig>, can you please change this before merging? Also, this is a nit, but newlines are inconsistent after headings and codefences, would be nice if we can be consistent with a single new line after each one