Add flux.driftDetection to JSON schema

The driftDetection property has been added to values.yaml but is not included in the JSON Schema. It works because additionalProperties is not set to false for the flux object but it would be kind to our users to at the very least add the driftDetection key and enforce the possible values via the JSON schema.

See: https://repo1.dso.mil/big-bang/bigbang/-/blob/master/chart/values.yaml?ref_type=heads#L127