OGM-521 Incorporating review remarks
OGM-595 Usability improvements around id generation strategies

* Setting AvailableSettings.USE_NEW_ID_GENERATOR_MAPPINGS by default in OgmConfiguration
* Making sure OGM's generators are used when working with the old generator mappings
OGM-595 Removing setting of property QUERY_STARTUP_CHECKING which is not required anymore
OGM-454 Moving internal types to "impl" packages
OGM-454 Moving SPI types to "spi" packages
OGM-454 Moving OptionConfigurator to API package
OGM-454 Avoiding FQNs in JavaDocs of public types
OGM-454 Marking GridType and GridDialect#overrideType() with @Experimental
OGM-454 Extracting interface from class ConfigurationContext to avoid leaking impl types on SPI contracts

* Also moving context base classes to "spi" as they are intended for usage in dialect modules
OGM-454 Splitting up ConfigurationPropertyReader into SPI and implementation part to avoid references from dialects to internal classes
OGM-454 Moving some types used in dialects from "impl" to "spi"
OGM-454 Moving AssociatedEntityKeyMetadata next to other metadata objects into "grid" package