Add an option to mount `airflow-site/sphinx_airflow_theme` when running CI locally

[shahar1]

Description

As of today, making changes in Airflow's site theme requires a lot of effort, as sphinx_airflow_theme is installed from PyPi:

airflow/hatch_build.py

Line 158 in 14f6622

"sphinx-airflow-theme>=0.0.12",

It doesn't happen often, but when we need to modify it for any reason (for example, as part of upgrading Sphinx version and related components - see this PR), we need to make a lot of workarounds to make it work.
Having the option to mount local airflow-site directory will make it way easier to test.

Use case/motivation

No response

Related issues

No response

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[potiuk]

As discussed on slack. One of the solutions is to add it our uv workspace in airflow and build it from there. I might want to take a stab with that one soon-ish.