Unify Beluga documentation

[hidmic]

Proposed changes

This patch unifies all repository documentation in a common Sphinx site: high-level documentation lives in MyST flavor Markdown documents, Doxygen API documentation is pulled in using the autodox extension in https://github.com/Ekumen-OS/sphinx-babel.

In the process, this PR partially addresses #301, #302, #303, #304, and #308.

Type of change

• 🐛 Bugfix (change which fixes an issue)
• 🚀 Feature (change which adds functionality)
• 📚 Documentation (change which fixes or extends documentation)

💥 Breaking change! This patch changes the way we used to build documentation for the Beluga package.

Checklist

• Lint and unit tests (if any) pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• All commits have been signed for DCO

Additional comments

This patch gets us 80% of the way towards release ready documentation. High-level documentation is not as polished as I would like to (specially the Key Concepts page), but this patch is big enough already and I'm too drained to produce quality technical writing. The easiest way to review this is building documentation locally and exploring it. You can check the README file under docs for instructions, or simply:

git clone https://github.com/Ekumen-OS/beluga.git
cd beluga/docs
python3 -m venv venv
source venv/bin/activate
pip install -r requirements.txt
make html 

Note this documentation needs Python 3.9 or later to build. I was not able to get all dependencies to play ball in earlier Python versions.

[nahueespinosa]

@hidmic This is absolutely amazing! I have a couple of quick questions about the setup before I start the review.

[hidmic]

Looks like Rolling moved on to Noble already and we are getting build failures 👀

[nahueespinosa]

@hidmic I love this! First pass, I'll continue the review later.

[nahueespinosa]

LGTM!

[hidmic]

Rolling CI failures will be fixed by https://github.com/open-navigation/navigation2/pull/4267. Going in!