Provide a migration procedure for MongoDB directories

Since NXP-21582 directories are now stored in MongoDB when appropriate template is enabled.

This will be an issue for users upgrading from LTS prior to 2017 to LTS 2017 which has the mongodb template.

As there's no real use cases to have directories stored in a SQL database when repository uses MongoDB, we need a (automatic) way to migrate data from SQL to MongoDB directories.

This could be a first step for NXP-21839.

The main case is to handle migration for directory contributions generated by the platform or by studio. As it was done in NXP-22785, we first contribute to SQL directory factory, and then this contribution is overridden by the MongoDB directory contribution.
But we keep a list of both contributions, so it's technically possible to get the former SQL directory descriptor. An idea would be to read this SQL directory contribution and then write its data in the MongoDB one.

The second case is to handle migration for directory contributions written by user, present under nxserver/config or in a marketplace package. These directories will need a manual upgrade, as the directory factory which receive contribution is not the same for SQL and MongoDB.