Creating this card to clean up the Feast Core and Feast Serving configuration files. The configuration files have the following problems

• No clear separation of static Spring or JVM configuration from user level configuration
• Duplicate configuration points for the same thing (BigQuery, or Dataflow configuration)
• Lack of documentation of the options that are configurable.
• Lack of documentation on where new configuration should be placed.
• [EDIT] Adding more scope to this refactor. Configuration should also be easy to define and pass to stores. Validation should happen at the storage layer, not in Feast Core or Feast Serving. This change should make it easier to support stores as interfaces, possibly with factories building the stores/retrievers based on configuration.

This issue tracks the refactor, cleanup, and documentation to solve the above.