GitHub Actions for MAPLv3 development

[mathomp4]

MAPL is working toward a version 3 that will have incompatibilities to MAPL 2. This branch is now on this repository called release/MAPL-v3 and will allow the SI Team to make changes to this repository while not affecting develop directly.

What this PR does is add a GitHub Action so that any push to develop (aka, any PR merged into develop) also automatically makes a PR from develop into release/MAPL-v3.

This way, our tracking branch can "keep up" with develop and once MAPL 3 is ready to go, all that is needed is to merge release/MAPL-v3 into develop and we are good.

Moreover, MAPL currently now does a build of GEOSadas with every PR. By having an "up-to-date" MAPL-3 ready branch here, we can also have that capability in our MAPL v3 development.

NOTE: This will add a bit of noise to GEOSadas where PRs like this:

GEOS-ESM/GEOSldas#524

will appear after merges to develop. The SI Team will take care of these when they happen as they are a reminder to us that we need to keep our release/MAPL-v3 branch up to date.

[tclune]

CI changes ok.

[rtodling]

Let me understand these .. if I pull them into develop and I am still using MAPL.2 ... will these break my use of MAPL 2?

[tclune]

The changes in this PR will not break anything. Later changes that directly accommodate MAPL v3 will go on a special branch. Those you should not merge into develop, and we will not be issuing any PR's like that to temp you. This change is to separately (and automatically) test such changes on the release branch.

[mathomp4]

Let me understand these .. if I pull them into develop and I am still using MAPL.2 ... will these break my use of MAPL 2?

Indeed, as @tclune says, all this is doing is setting things up so we can work on MAPL 3 changes without having to go near develop or main. We'll be on our own branch. But these updates allow us to essentially get "notifications" that develop has changed, so we know that we then need to merge these in to our branch.

The hope is that in XXX months, when MAPL 3 is ready, all we have to do is pull our branch into develop and boom you have a MAPL 3 ready GEOSadas!

[rtodling]

I will trust both of you (Matt & Tom) on this ...