Support empty rhsm_url setting on proxies

[ekohl]

What are the changes introduced in this pull request?

This drops the compatibility fallbacks that were in place for pre-3.1
installations. Since then the value has been present.

Now it becomes possible to not set a value which means the RHSM URL is
on the Foreman instance itself. This is useful for Pulp-only
installations without any RHSM reverse proxy setup.

Considerations taken when implementing this change?

We don't care about pre-Foreman 3.1 installations and this is long term to support the use of standa lone Pulp proxies via https://github.com/evgeni/pulp_smart_proxy.

For now this is a draft because I'm looking for feedback if this is a good idea at all.

What are the testing steps for this pull request?

There are unit tests (which I don't think will pass). It also doesn't cover the nil vs empty string, which should be handled via .presence.

[evgeni]

Isn't that recursive now?

[ekohl]

I think it is. I hate Rails' URL helpers

[evgeni]

Sure, but where should rhsm_url come from even w/o Rails?
I think the following should work?

def rhsm_url
  if (rhsm_url_setting = setting(SmartProxy::PULP3_FEATURE, 'rhsm_url').presence)
    URI(rhsm_url_setting)
  else
    URI("https://#{URI.parse(url).host}/rhsm")
  end
end

[ekohl]

Rails itself should be able to look up the route and generate the url. The whole change here is also that it's the Foreman URL now, not on the proxy. Essentially making it opt in whether there is a reverse proxy for RHSM

[ekohl]

I ended up using the foreman_url setting and hardcode the path instead of figuring out the URL helpers. They don't appear to be included in the helper and passing in context is going to be too hard (and possibly wrong).