DEV: Update CustomPropertiesConfiguration to pull from DB

**CustomPropertiesConfiguration currently reads custom entity attributes from attributes.yml - these are transformed from the file into: 

RelyingPartyOverrideProperty objects.

1. Refactor CustomEntityAttributeDefinitions - to be RelyingPartyOverrideProperty (or some such - these are essentially the same) - make RPOP an interface and the values saved to the DB should implement it - the stuff from the config file implement something else that spring fills in from config file
2. Update CustomPropertiesConfiguration to read from the DB in addition to the configuration. Note that DB definitions should override configuration from the attributes.yml file