Move Pinot configs management to helix

The purpose here is to minimize the config requirement for pinot deployments and simplify the config management.

To achieve this, we can move all the common/default configs to helix as cluster configs.
Also, this change should not prevent users to start pinot using config files or setting env variables.

In my view, when a pinot server starts, it will:
1. Look up helix for global configs as base
2. Apply helix participant configs
3. Apply the config files
4. Apply the environment variables.

Btw, if we start Pinot using the service manager wrapper, then we can actually achieve server restart using API calls to pickup new global configs.

@kishoreg @mayankshriv