Initial schema changes for tenants and numeric_data tables

Here are the schema changes based on my [design document](https://docs.google.com/document/d/1Il9wHSKQD4QwVmgmZhrA7ghRejAt2Qka98_qoQFDfUU/edit?usp=sharing). This PR includes implementation for the numeric_data table which replaces the metrics table, and an initial implementation for the tenants table. It is functionally equivalent with what is in master today. All unit and integration tests are passing.