Remove SystemEntitlementManager as proxy context parameter and reorga…

[rjpmestre]

What does this PR change?

This PR is a follow up on a comment. In short, we're removing a couple of parameters from proxy-related class constructors that were mainly used to support testing and are no longer needed, as we’ve found a suitable workaround.
Also, taking the oportunity of the recent maven update and file organization/restructure to reorganize proxy suitable subpackages.

Codespace

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GUI diff

No difference.

• DONE

Documentation

• No documentation needed: only internal and user invisible changes

• DONE

Test coverage

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• No tests: already covered

• DONE

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Acceptance tests will take some time (aprox. 1h), please be patient ☕

You can see the progress at the end of this page and at https://github.com/uyuni-project/uyuni/pull/11246/checks
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Reference tests:

• https://github.com/uyuni-project/uyuni/actions/workflows/acceptance_tests_secondary_parallel.yml?query=event%3Aschedule

• https://github.com/uyuni-project/uyuni/actions/workflows/acceptance_tests_secondary.yml?query=event%3Aschedule

KNOWN ISSUES

Sometimes the build can fail when pulling new jar files from download.opensuse.org . This is a known limitation. Given this happens rarely, when it does, all you need to do is rerun the test. Sorry for the inconvenience.

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Happy hacking!
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[cbosdo]

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Also add the description of the PR as the commit message: your future self (or anyone else) will thank you for that when digging later.