Add agora / our dependencies to the project tester

[bpalaggi]

As a Developer, I need the Dlang project tester to test Agora in order to catch regression before they’re introduced.

[Geod24]

dlang/ci#394

[Geod24]

In order to be useful, this would require a rather large rework of the project tester.
In particular, the project tester is specific to a single platform, and tied to Travis. Having it execute Github actions, cross platform, would be much better in the long run.

I think a good devops with knowledge of Github actions might be able to implement most of the required functionalities in 2 sprints, but it's still a lot of work to put upstream.