[Database] Switch to cascading deletes in the DB layer where possible + some cleanup (#4312)

* Switch to cascading deletes in the DB layer where possible.

* Remove extra ON DELETE CASCADE from artifact_branches table.

* Restore ON CASCADE DELETE for h2 and pg on FK_artifact_branches_1

* Restore functionality of deleteGroup: there is no FK from artifacts to groups yet

* Use consistent column names for names/keys and values

* Rename prop_name and prop_value in validate-files.sh

Author: EricWittmann

app/src/main/java/io/apicurio/registry/storage/RegistryStorage.java

@@ -568,7 +568,7 @@ void updateArtifactRule(String groupId, String artifactId, RuleType rule, RuleCo
     void updateGroupMetaData(GroupMetaDataDto group) throws GroupNotFoundException, RegistryStorageException;
 
     /**
-     * Deletes a group intified by the given groupId and DELETES ALL resources related to this group
+     * Deletes a group identified by the given groupId and DELETES ALL resources related to this group
      *
      * @param groupId (optional)
      * @throws GroupNotFoundException