cubicweb #1631339 support for database namespaces [validation pending]

add a source config option to define a database namespace and pass the information to lgcd.connect()

prioritynormal
typeenhancement
done in3.20.0
load1.000
load left0.000
closed by#bc6461a7d2da [server] add a db-namespace option in source definition (closes #1631339)
patch[server] add a db-namespace option in source definition (closes #1631339) [applied][server] refactor cleanup() code used by "cubicweb-ctl delete" [applied]