Cleanup for build

[SandersAaronD]

The current github actions build references several scripts that belong to me personally, which I was hoping to upstream with the plugins platform team. The second part of this has not happened, which leaves us in the awkward position of having somewhat important build infrastructure in my personal github, where it was only supposed to be temporarily.

Given that these should not be in my personal repo, and they are over-designed and clunky for our team to maintain if they are not going to be upstreamed anywhere, we should switch these over as far as possible to calls to grabpl. An example exists here.

I think the only github action we actually need from my personal repo is publish-plugin-on-site, which should be relatively simple to move over into a raw workflow file (since it is just bash).

The end result is really simple but such a setup would ideally get a lot of testing because all of the variables etc would be different and prone to breakage.