Default deployment of service monitor does not have valid credentials

As part of !75 (merged) - we added a metrics user to remove the need for admin credentials to be used for metrics authentication (and therefore removing the need to store admin credentials for nexus in the cluster).

While we documented guidance for new installs and upgrades here - the out-of-the-box behavior for this package will leave the consumer with a missing target in prometheus and invalid authentication credentials for the servicemonitor resource.

There are two identified paths we can execute on:

• add a conditional to the servicemonitor such that it can be enabled/disabled separately of the monitoring settings.
• add logic to the servicemonitor to use admin credentials for the auth by default and the ability to switch between which credentials are used (more complexity but establishes a more complete default baseline).