Propose a way to execute custom queries when provisioning a partition

[ylegat]

Is your feature request related to a problem? Please describe

Currently, when privisioning a partition, the manager can only add constraints that are defined on the partitioned table.
But some constraints cannot be configured on the partitioned table and some users might still want the on their partitions.
That is the case of unique constraints that do not include the partition key.

However, adding a unique index on each partitions does not guarantee the unicity of the value globally (among all partitions).
So it is not clear if it is worth enabling this possibility just for that case.

Describe the solution you'd like

The more flexible solution would be to allow users to define custom query to be executed during the provisioning of a partition.