ci: use github action for bulk of github test

[rfay]

The Issue

We now have the lovely github-action-add-on-test from @julienloizelet - THANKS!

This uses it.

[rfay]

Please confirm correctness @julienloizelet @tyler36

I also implemented this in ddev-platformsh

[julienloizelet]

Thanks @rfay ,

• We could remove the defaults part : https://github.com/ddev/ddev-addon-template/blob/f1d038d8ed87bf48baa7ce0998ce5343ec0ac36e/.github/workflows/tests.yml#L28-L30

We already set bash as shell in every step of the action because it is required to define one : https://github.com/ddev/github-action-add-on-test/blob/main/action.yaml#L63 for example

• We could remove the env part https://github.com/ddev/ddev-addon-template/blob/f1d038d8ed87bf48baa7ce0998ce5343ec0ac36e/.github/workflows/tests.yml#L22-L24

The DDEV_GITHUB_TOKEN value is already set in the action: https://github.com/ddev/github-action-add-on-test/blob/main/action.yaml#L98-L100

There's no harm in keeping it, but :

• the fewer things there are outside the action, the less maintenance is required
• If someone set the DDEV_GITHUB_TOKEN value outside the action, it will be overridden in the action by the token input value.
• Everyday, this run https://github.com/ddev/github-action-add-on-test/actions/workflows/add-ons-test.yml launches about 20 quasi simultaneous ddev get without reaching the API rate limit (It doesn't prove anything, but it suggests that it works.).

[rfay]

See what you think now @julienloizelet - thanks for paying careful attention.