lakeFS Database migration

[N-o-Z]

Support migration of lakeFS database between different KV implementations by adding 2 flows:

1. Export - dump all the data from old database into file
2. Import - load data from file to the new database

Database migration will be allowed only on the same lakeFS version

Import was already implemented as part of the Postgres KV migration What's left is to add the export functionality and add the required validations

Open question:

• What should we do with the lakeFS metadata? Consider the scenario where data is exported from one system and imported to another. Do we want to support it?