redhat_subscription: drop unneeded args to Rhsm.register() (#5583)

Stop passing all the "rhsm_", and "server_" module arguments to
"Rhsm.register()", and thus as arguments for
"subscription-manager register":
- right before calling "Rhsm.register()", "Rhsm.configure()" is called
  to configure subscription-manager with all the "rhsm_", and "server_"
  arguments; hence, they are already configured
- the passed argument to "--serverurl" is partially wrong:
  "Rhsm.register()" passes only the hostname, whereas the other bits
  (port and prefix) are supported too; this "works" because port and
  prefix were already configured previously, and the lax parsing that
  subscription-manager does allows for missing bits
- the parsing done by subscription-manager for "--baseurl" strips out
  the URL scheme and always uses https: this means that specifying
  "rhsm_baseurl: http://server" as module parameter will be taken as
  "https://server" by subscription-manager; since "rhsm_baseurl" is
  already configured by "Rhsm.configure()", this issue is gone

changelogs/fragments/5583-redhat_subscription-subscribe-parameters.yaml

@@ -0,0 +1,3 @@
+bugfixes:
+  - redhat_subscription - do not pass arguments to ``subscription-manager register`` for things already configured; now a specified ``rhsm_baseurl`` is properly set for subscription-manager
+    (https://github.com/ansible-collections/community.general/pull/5583).