Add versioning to User Docs

[Santonia27]

Currently the versioning of the Docs is disabled in the workflow (commented out in the Deployment to gh-pages section).

As soon as the docs are done and we start versioning in Floodadapt we should look into the versioning of the docs again.

Couple online docs to releases of FloodAdapt and FloodAdapt-GUI

[Santonia27]

echo "DOC_VERSION=$(mamba run -n fiat_docs python -c 'from fiat import version as v; print("dev" if "dev" in v else "v"+v.replace(".dev",""))')" >> $GITHUB_ENV

line copied from Delft Fiat repo. Add this to docs workflow and uncomment #destination_dir: ./${{ env.DOC_VERSION }}