Handle report deployment

[JavierCladellas]

Add workflows to handle accepting/denying upcoming benchmarks via PRs.
Idea:

• benchmark.yml (on dispatch event) will upload results to a staging/ folder on Girder (or gaya, to be defined) , then will create a PR.
• preview_website.yml (on PR event) will render ONLY benchmarks that are under staging/
• deploy.yml (On merge to main). Will move reports from staging/ to production/, and update the website_config.json file to add latest accepted reports.
• cleanup.yml (maybe not needed? On PR close event) : will move benchmarks from staging/ to denied/ .

These PRs should be tagged by a specific keyword to make the difference with dev PRs.
Maybe add a date to index.adoc to have a changed file on the git tree.

@prudhomm @vincentchabannes Thoughts? Do you have a simpler workflow in mind ?