Implement several legalhold along with description

As described in NXP-27385 we need to implement the ability to set several legal holds on the same documents.

The new setLegalHold method from core session allows to only create one single hold.

The retention addon should add an implementation on top on that to set many legal holds and as long as there is one set, the core session one will remain.

It involves the ability to store a description for each legal hold along with the user who set it.

Finally, we should have a distinct UI permission Manage Legal Hold different than Manage Record (to attach rule)