Upstream: stable/grafana to accept template for user/password secret

Summary

As a part of the research & development in !789 (merged), to close #1159 (closed), we found that upstream stable/grafana has the ability to take an external secret for initial username & password configuration, it can only do so with static properties.

For our use, we should implement the functionality to pull this information from a template in order to insert default values that align to the secret generation that we make use of.