Add moodle ci GHA

[aspark21]

This is based on the template - https://moodlehq.github.io/moodle-plugin-ci/

With a matrix we use that covers a wide range of Moodle versions

While this currently fails - https://github.com/ucl-isd/moodle-mod_turnitintooltwo/actions/runs/10103239505

This is something our devs find useful to find things broken by new versions of Moodle

Should help with knowing what maintenance is required

To get it working, you'd have to look at the npm dependencies which seem to cause the install step to fail - https://github.com/ucl-isd/moodle-mod_turnitintooltwo/actions/runs/10103239505/job/27940251623#step:6:47

[jack-tii]

Thank you for this PR, this is a feature I would love to have.
We are currently having some internal discussions about the best way to implement this, and I will let you know when a decision has been made. Merging this will therefore have to wait until after the next release, which is currently scheduled for August 1st.