JENKINS-61654: allow customization of used SCMRevision

[dev-hanz-ops]

This PR addresses JENKINS-61654 and is an improved version of #155

The original PR was created to make this plugin use the revision of an upstream job, if a build was triggered using the build step.

Contrary to #155, this one is more flexible:

• The determination of the SCMRevision is not hardcoded in this plugin, so that it can be used for more than just upstream/downstream builds
• Plugins can create such behavior/trait for any SCMSource (not only GitHub)
• Behavior can be turned on & off by the user

Also, no additional pom dependency is required, as everything is handled in newly-created plugins. One example for such a plugin is the (not yet published) github-upstream-revision-plugin

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