Authentication to Cluster Manager

In production environments, the Cluster Manager cannot be exposed to all users as-is, because it contains operations which can change the state of Pinot. The goal is to add basic authentication and have roles like admin and read-only.

We need to begin by enabling security on the controller port, and then make some UI changes to add login.

Begin by tracing how security is configured on the controller port and where the Cluster Manager UI handles access. Define the authentication and admin/read-only role requirements before changing both areas; done means the controller is protected and the UI provides login with those roles.

Written by the indexing model from the issue text.