Linkage Checker to work without touching the user's .m2 cache?

(Not decided to work on this yet but filing it as an idea)

Kenn's comment in https://github.com/apache/beam/pull/10184#discussion_r349283259

> Can we publish somewhere under build/ instead, or to a tempdir, so that we don't have to install to the user's .m2 cache?

Idea is, by using somewhere else than user's .m2 cache, it will be easy to cleanup the side effect of LinkageCheckerMain.

Think about a scenario where a user (Beam Developer for example) suffers from their .m2 cache having these artifacts and their dependencies.

Start by reading LinkageCheckerMain and the linked pull request discussion about publishing under build/ or a tempdir instead of the user's .m2 cache. Determine the intended artifact location and cleanup behavior; the issue is done when LinkageCheckerMain no longer leaves artifacts and dependencies in the user's cache.

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