Update Docs on changing the Grafana credentials

Package Merge Request

Package Changes

The current doc incorrectly instructs users to change Grafana password through the monitoring.values.grafana.adminPassword values when it should be changes through grafana.values.adminPassword.

Package MR

NA

For Issue

Closes https://repo1.dso.mil/big-bang/product/packages/monitoring/-/issues/243

Upgrade Notices

N/A

Closes #243 (closed)