Flexible retention behavior

As a record manager, I can pick the flexible retention option for a given rule

AC
When a document goes under retention with a rule using this option

• All protected blobs from the document are stored in the regular storage bucket
• The retention can be unset on the record (i.e., I can stop retention if I have the appropriate permission, see other stories)
• The record can be put on legal hold (similar to existing behavior)
  • Putting the record on legal hold means that
    • the files are copied into the dedicated retention bucket (if it exists) and put under legal hold
    • the record becomes enforced and it is not possible to turn the record back into flexible mode
  • When removing legal hold, file remains in the dedicated bucket and legal hold is removed
• Retention can be extended, not reduced (similar to existing behavior)