Add and handle billing data service

[mcalmer]

What does this PR change?

The billing-data-service is needed for SUMA PAYG Public Cloud image.
As we do not want a special container, we install it by default inside of the container and enable the service.

The service has a condition to only start when ISPAYG environment variable is set. This should be done by "mgradm install"
via the service file.

GUI diff

No difference.

• DONE

Documentation

• No documentation needed: only internal and user invisible changes

• DONE

Test coverage

• No tests: already covered

• DONE

Links

Issue(s): https://github.com/SUSE/spacewalk/issues/24287

• DONE

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[deneb-alpha]

I left a few comments

[cbosdo]

This looks good to me. Do you already have a PR for uyuni-tools setting the ISPAYG variable?

[mcalmer]

This looks good to me. Do you already have a PR for uyuni-tools setting the ISPAYG variable?

No, and I will wait with merging this one until we have it.