Use https instead of git protocol in pip install

We are depending on grafana-dashboard-builder to export dashboard manifests programmatically. The support for python 3.8+ for this library is available on GitHub, but not yet published as a new version to PyPI, so we need to install it via pip git+<git_url> to have access to this newer version.

However, the Github has changed some infrastructure configuration recently, and do not permit to clone via git:// protocol anymore, luckily https:// is still working.

Besides, this MR adds a requirements.txt file to be easier to maintain pip libraries dependencies in this project.

Fixes this error: https://gitlab.freedesktop.org/gallo/mesa-performance-tracking/-/jobs/19954943#L1126