Move CI and documentation from GitLab to GitHub

[bmazurie]

Move CI and documentation from GitLab to GitHub

ThermoSysPro is now hosted on GitHub. This PR moves the OpenModelica tests and the documentation to GitHub Actions. The Dymola tests stay on the internal GitLab runner.

Changes

• OpenModelica tests (.github/workflows/openmodelica-tests.yml): the Examples models are tested with ModelicaTests and compared with the PR target branch (develop or master). The run summary lists regressions, fixed models and changed results. The HTML/CSV reports and the OpenModelica logs are uploaded as artifacts. Works like the TAeZoSysPro workflow (.test/report.py comes from there).
• Documentation (.github/workflows/documentation.yml): the Jupyter Book is generated from the Modelica annotations and deployed to GitHub Pages (https://edf-lab.github.io/ThermoSysPro/).
  ⚠️ For now it is also deployed on each PR, to test the workflow. The TODO comments mark what to change to deploy master only.
• GitLab CI: only the internal Dymola job is kept (ThermoSysPro_mirror).
• Links: README, ContributionsWorkflow.md (GitHub issues, pull requests, CI description), issue templates moved to .github/ISSUE_TEMPLATE/, Jupyter Book repository URL.

Repository settings needed

• Secret MODELICATESTS_TOKEN (read access to ModelicaTests). Optional variable OPENMODELICA_IMAGE.
• Settings > Pages > Source: GitHub Actions.
• Settings > Environments > github-pages: allow all branches while PRs are deployed.
• Internal: point the ThermoSysPro_mirror pull mirror to GitHub.