There should be an "OpenOptions" argument to DB::Open for "open time" parameters

There should be a separate "OpenOptions" to the DB::Open API that can be used to control how the database is opened. Examples of values in the OpenOptions could include:
- Open the DB for ReadOnly or not
- Open the DB as a Secondary

Some existing parameters (that make no sense in an Options file) could also be moved into the OpenOptions:
- create_if_missing
- error_if_exists
- create_missing_column_families

The OpenOptions could also be used to help/advise when opening a Checkpoint (or a different database copy) on whether to override file paths to a different location.