[to discuss] merge of databases

Currently DIRAC(X) defines and use several databases. Some of these have clear relations one to the other, i.e.:

- WMS

JobDB
JobLoggingDB
PilotAgentsDB
SandboxMetadataDB
TaskQueueDB

- Productions

TransformationDB
ProductionDB

We should consider merging these databases together, as this would give us, at a minimum, the possibility to actually define the FOREIGN KEYS (`JobID` is a clearly "everywhere" in the WMS DBs), with all the consequences of it (consistency, at a minimum)