Update docs to mention the need for logging into Harbor before running umbrella

I think it would be useful to mention the need for manual logins or robot accounts further up in the docs. I just now found https://repo1.dso.mil/platform-one/big-bang/umbrella/-/blob/master/docs/b_troubleshooting.md#iron-bank-authentication which solved issues we were having earlier. Ideally the need for manual logins or contacting someone for a production account would be mentioned in the deployment doc or the configuration doc under registryCredentials since that is a requirement for running big bang / umbrella