Review kogito-ddl content

Checking the content of the current kogito-ddl-db-scripts, I can suggest a few enhancements:

• remove exists_tables.sql as this is not part of DDL
• We currently got the following set of archives:
  • create.sql
  • V2.0.0__Create_Table.sql
  • create_tables.sql

           That's a bit confusing to identify which service it belongs to, so my suggestion would be to rename these to the following

• data_index_create.sql
• jobs_service_create.sql
• runtime_create.sql