Make the Dependency Tree Input Builder workflow a bit more modifiable

The 'Dependency Tree Input Builder' github workflow makes it difficult to modify the source tree because it hard codes a list of expected modules and fails if they are not present. It should cleanly handle non-existent modules, both in the base branch and in the PR branch.

It's still problematic to modify the source tree by adding new modules to check, as it's the workflow yml in main that executes, not the one in the PR. But that can be worked around by the one doing the modification by doing a dance of adding the planned new modules to check in one PR and, once that is merged, adding the actual new modules in another PR.

As part of this work I will add the planned modules for WFLY-17684.