.github: Add destination depth to doc build

[gastmaier]

This repo stores different versions of the doc into multiple directories of the gh-pages branch.
Due to this, links requiring to reach the website root (not the content root of the doc itself), are broken if the deploy directory is different than ./ (e.g. ./main, ./prs/1234)

To resolve this issue, the ADOC_TARGET_DEPTH env variable was implemented analogdevicesinc/doctools@1da4cf1 to allow tuning the depth before the doc build.

Example of ADOC_TARGET_DEPTH values:

• ./ : ../ (0 or unset)
• ./main/ : ../../ (1)
• ./prs/1234 : ../../../ (2)

On Doctools I also added a snipped to generate a JSON with the tags/branches/prs of the build docs, but since this repo uses peaceiris/actions-gh-pages@v3 action to commit and push to gh-pages, I didn't implement it here.
However, this tags.json file would be nice to create a dropdown to switch between versions on the live doc.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How has this been tested?

This feature was tested on the Doctools repo itself, with different builds linking properly:
https://analogdevicesinc.github.io/doctools/
https://analogdevicesinc.github.io/doctools/v0.3.38/

Then I tested different values of ADOC_TARGET_DEPTH while building this repo doc locally.

Documentation

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have signed off all commits and they contain "Signed-off by: "
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[github-actions]

Generated documentation for this PR is available at Link

[github-actions]

Test Results

1 600 tests  ±0     357 ✅ ±0   12m 5s ⏱️ +21s
    1 suites ±0   1 243 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 8366cdc. ± Comparison against base commit 764dd5b.

♻️ This comment has been updated with latest results.