Unify ospo-actions configuration

Currently, the various ospo actions are completely independent. But users who adopt several of them end up restating a lot of configuration for them which would ideally be centralized. As concrete examples, setting:

* a list of repositories to ignore from reporting, or conversely a list of ones to _only_ report
* whether to execute in dry run mode or not
* output formats / destinations that are not the default
* ... probably others ...

would be better served by a common configuration file that all of the actions know to look for.

Start by cataloguing the existing ospo actions and how each currently receives configuration; no files or entry points are named in the issue. Compare their handling of ignored or included repositories, dry-run mode, and output formats or destinations. Done means the actions can use a shared configuration source without repeating these settings.

Written by the indexing model from the issue text.