Use https to access the API in spacewalk-common-channels and mgr-sync

[cbosdo]

What does this PR change?

In some cases the http port seems not available for the XML-RPC API. Use http://localhost:80 by default for those tools and https when using the server's FQDN.

Using localhost helps reducing the possible hairpins when running in a container environment.

GUI diff

No difference.

• DONE

Documentation

• No documentation needed: only internal and user invisible changes

• DONE

Test coverage

• No tests: tools defaults, partly covered by e2e tests

• DONE

Links

Fixes #5565

• DONE

Changelogs

Make sure the changelogs entries you are adding are compliant with https://github.com/uyuni-project/uyuni/wiki/Contributing#changelogs and https://github.com/uyuni-project/uyuni/wiki/Contributing#uyuni-projectuyuni-repository

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[github-actions]

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[vzhestkov]

In general the change is good for me, but just one nitpicky suggestion inline just to make the code more readable.