Anchor tag bugs

[bmorelli25]

Bug summary

Bug 1

What happens
Anchor tags are only generated for H1 and H2 level headings.

What I expect to happen
Anchor tags should be generated for all heading levels.

Bug 2

What happens
If a heading includes backticks, the ID is not unique or correct. For example, the heading ## `note` creates the following anchor: markdig.syntax.inlines.codeinline. This also impacts the OTP (on this page) widget on the right side of the page:

What I expect to happen
Backticks should be ignored and a unique anchor tag should be created.

Bug 3

What happens
Linking to valid anchor tags on a different page fails the link checker. For example:

[Notes](tables.md#notes)

Error: `notes` does not exist in .
    ┌─[/github/workspace/docs/source/syntax/links.md]
    │
 [35](https://github.com/elastic/docs-builder/actions/runs/12638318856/job/35214323557?pr=129#step:4:36) │ I link to the [Notes](tables.md#notes) heading on the [Tables](tables.md) page.
    ·              ───────────────                                                   
    ·                                                                                 
    │
    └─
	1 Errors / 0 Warnings

:: info: Program[0] generate :: Finished in '00:00:00.0220[37](https://github.com/elastic/docs-builder/actions/runs/12638318856/job/35214323557?pr=129#step:4:38)5

What I expect to happen
The link checker should not fail on valid anchor links.

[bmorelli25]

Another bug:

Linking to headings across pages doesn't work. For example, this link:

I link to the [Notes](tables.html#notes) heading on the [Tables](tables.html) page.

Takes users to:

http://localhost:5000/syntax/tables.html#notes#notes

[bmorelli25]

Never mind on the above comment. I was using .html instead of .md. The original bug still stands.

[bmorelli25]

Update to the update:

The link renders and works correctly in the product when you use .md, but the link checker fails:

[Notes](tables.md#notes)

Error: `notes` does not exist in .
    ┌─[/github/workspace/docs/source/syntax/links.md]
    │
 [35](https://github.com/elastic/docs-builder/actions/runs/12638318856/job/35214323557?pr=129#step:4:36) │ I link to the [Notes](tables.md#notes) heading on the [Tables](tables.md) page.
    ·              ───────────────                                                   
    ·                                                                                 
    │
    └─
	1 Errors / 0 Warnings

:: info: Program[0] generate :: Finished in '00:00:00.0220[37](https://github.com/elastic/docs-builder/actions/runs/12638318856/job/35214323557?pr=129#step:4:38)5