Use a custom Hubzilla image to speed up pipeline.
Single test jobs were around 4:30-5:00 minutes, now ~1:30 minute.
Improve Composer cache in Gitlab CI/CD.
Add more recent databases (MySQL8, MariaDB10.3) to the pipeline.
Create the API documentation with Doxygen and
publish it through gitlab-ci as a Gitlab page at:
https://hubzilla.frama.io/core
This should only happen when master gets updated.
Update Doxyfile configuration. Correct image usage.
Replace RedMatrix with Hubzilla icon.
