Link checker fails on anchor links within other elements

[bmorelli25]

Summary

I'm seeing the following error when building the ES Guide:

Error: `es-connectors-s3-usage-create-iam` does not exist in es-connectors-s3.md.
     ┌─[/Users/brandon/Documents/GitHub/elasticsearch.md/docs/es-connectors-s3.md]
     │
 124 │ S3 users will also need to [Create an IAM identity](es-connectors-s3.md#es-connectors-s3-usage-create-iam)
     ·                           ─────────────────────────────────────────────────────                           
     ·                                                                                                            
     │
     └─

This error indicates that:

1. in the /es-connectors-s3.md file
2. there is a link to es-connectors-s3.md#es-connectors-s3-usage-create-iam
   I can verify this is correct:

However, the link checker fails saying that the anchor does not exist. This is happening because the anchor lives inside of a collapsable block. Note that the anchors do work just fine when clicked on the page:

Steps to repro

1. dotnet publish "src/docs-builder/docs-builder.csproj" && ./.artifacts/publish/docs-builder/release/docs-builder serve -p ../elasticsearch.md
2. Visit http://localhost:3000/es-connectors-s3.html#es-connectors-s3-usage-create-iam

[reakaleek]

This could be fixed by #349.

But I think there is the question if we actually want to support this. In the current implementation, this means, that these headers also added to right "On This Page" table of contents.

(I have a feeling the original implementation only considered top level headings on purpose)

Not sure if this is desired.

WDYT?

@Mpdreamz?

[reakaleek]

As discussed merging it for now. We might revisit this in the future. Follow-up issue: #352