Draft: Deployment of a documentation using direct commit to the website

Motivation

We want to get rid of ReadTheDocs and use Gitlab Pages for hosting documentation.

Proposal

Gitlab Pages allows us to host only one version of documentation, therefore we need to some tricks. Shortly, my plan is the following:

1. From quantify-core and quantify-scheduler pipelines (and later quantify) we commit built documentation directly to this repo instead of deploying it via Pages for main and for version tags.
2. CI in this repo scans available documentation versions and generates JSON in the format required by pydata-sphinx-theme.
3. In the end, documentation gets deployed to https://quantify-os.org/docs/quantify-core/latest for main and to https://quantify-os.org/docs/quantify-core/vX.Y.Z for tagged releases, and can be selected with the dropdown.