Allow user created secret to stand in for plain text DB connection string in values file

[Ansible-man]

This chart should allow the user to create their own secret for the DB connection string. With the current way its setup you cant even override it with the MM_SQLSETTINGS_* env vars that the application should respect. Either A the chart documents this ENV var as a supported option and gives the option to not template the existing DB secret that gets creates either way or B this chart gives an option to create and reference your own secret containing the string. I am willing to put a PR in to support either option including the doc updates. We do not what to commit our DB connection string to source control. Given the other charts support this not sure why it would be an issue.

[Ansible-man]

This is for teams edition chart