[New Feature]: Allow multiple manifest deletions in single PR

Description of the new feature/enhancement

In the current situation, in order to delete the manifest of a version of a package, a PR needs to be created with the deletion of the appropriate files for that version and if multiple versions should be deleted, a PR has to be raised for each of them separately, since the bot pipeline requires that only one package is modified.

I think that it should be possible to delete multiple versions in one go (e.g. #83292) instead of having to create a separate PR for each version, as this takes more time for everyone involved.

I know that some people would argue that manifests should not be deleted if the source could still be accessed, but I can see different places where this would come handy or necessary. For example, old testing versions that are missing security features, or breaking changes of a backend which are not backward compatible with versions too far behind.

Proposed technical implementation details (optional)

I see two possibilities to deal with that:

1. Create a type of PR aimed only at version deletions: this would be done by requiring an appropriate string at the end of the PR name to be added (something like [version deletion]), which would trigger the different testing pipeline than the usual to only verify that the whole folder is appropriately deleted (not leaving a partial manifest behind).
2. Modify the testing pipelines, so that deletions are counted separately from manifest creation/modification: this would mean that the pipeline would first verify that all deletions correspond to full versions, and if this pass accordingly, it would only look at the remaining created/modified files and run in the usual way.

I am aware that each of these might involve quite some work in one way or another, and have both their pros and cons. The main advantage of 1. that I see is that it will save resources by not running the full testing pipeline, but a much simplified version, while option 2. has the advantage of not changing the current workflow of the PRs through the wingetbot and involve "only" a change on the testing pipeline flow.

There are probably other (possibly better) ways to implement that, but I would be happy to see this coming forward, which would allow to unclutter a bit the manifest folder.
Thanks.

No files or tests are named. Start by tracing the wingetbot workflow and the testing pipelines that enforce one-package changes, then compare how manifest deletions and other modifications are validated. Done means one PR can delete multiple complete package versions, rejects partial deletions, and still validates any remaining created or modified files.