Make VCS plugins configurable

[sschuberth]

While VCS implementations already are plugins, they are not configurable yet. As VCS both require configs that are common to all VCS implementations, e.g.

ort/downloader/src/main/kotlin/VersionControlSystem.kt

Lines 166 to 169 in d53ac0b

	/**
	* The priority in which this VCS should be probed. A higher value means a higher priority.
	*/
	protected open val priority: Int = 0

but should also be able to get implementation-specific configuration, probably an approach like with PackageManagerConfiguration would be feasible.

Having such configuration would probably help to address the following related issues

Tasks

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1. Make recursive cloning (e.g. of Git submodules) configurable #6697
   configuration downloader enhancement scanner +4
2. Configurable URL replacements for the analyzer / downloader #6698
   analyzer configuration downloader enhancement +4