Simplifies integration docs

[discdiver]

• Fixes minor build errors that already existed
• Links to SDK docs for each Prefect integration library
• Simplifies navigation
• Improves IA of integrations home page

Closes 13927
Closes 13928

Still to do in other PRs:

1. Create integration library images section with existing script to show Prefect-maintained and third-party images with links.
2. In contributing section, could improve example of creating a custom block or point elsewhere to show the user how to do that.

Example

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• If this pull request adds new functionality, it includes unit tests that cover the changes
• This pull request includes a label categorizing the change e.g. maintenance, fix, feature, enhancement, docs.

For documentation changes:

• This pull request includes redirect settings in mint.json for files that are removed or renamed.

For new functions or classes in the Python SDK:

• This pull request includes helpful docstrings.
• If a new Python file was added, this pull request contains a stub page in the Python SDK docs and an entry in docs/mint.json navigation.

[billpalombi]

Great stuff!