This improvement permit to store the recording type in the low-level table, we need a flag to identify if the uuid is an MBID or is generated in in the AB server.

It is connected with the possibility of submissions without MBID.
The details are visible in the documentation of the GSoC project: https://docs.google.com/document/d/1wVkJFvGzzINMSORVcGYZEI27kXAgKcAKwsRE3yyxHeE/edit#bookmark=id.9m7qf9s439lx

Actions:
-Add a field to the low-level table
-Create an index for this field (not mandatory)
-Add an upgrade sql script
-Modify the schema creation sql script