Update SCC REST call to register systems in bulk

[rjpmestre]

What does this PR change?

Update the current SCC system registration mechanism. Currently, it uses a SCC REST service that registers one system at a time. We are replacing it with a more efficient service that can handle bulk registrations.

GUI diff

No difference.

• DONE

Documentation

• No documentation needed

• DONE

Test coverage

• Unit tests were added

• DONE

Links

Implements https://github.com/SUSE/spacewalk/issues/17456

• DONE

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[github-actions]

Suggested tests to cover this Pull Request

• allcli_sanity
• srv_sync_channels
• srv_disable_local_repos_off

[parlt91]

The code itself looks good to me. However I am not familiar with SCC system registration at all. So I'd advise a second review from someone who knows the code better.

Also there is some failing acceptance tests related to removing system groups. Not sure if they are related but they could be. Please have a look before I approve.

Also your most recent changes seem to have broken your added java tests