Create & Integrate ServerStatus Interface For Global Index Metrics

We should create placeholder functions to handle the appending the metrics in response to a serverStatus request. Then integrate said placeholder functions into the serverStatus logic.

This should work for both resharding and global indexes.

• Add reportForServerStatus(...params)
• Add the scaffolding for the role logic
• Set all values to some reasonable placeholder for that type
• Add constants for the key names (not previously added by other work)