[TASK] Add `status` column to `records` table

[jfcalvo]

We should add status column to records table with the following details:

• Possible values for this status column are pending and completed.
• This new column will be non-nullable.
• It will have a database index so it will be faster to recover records with one specific status value.
• By default the status column will have the pending value. (Showing that the record is still pending of being annotated).
• Existent old records will be migrated in the following way:
  • Records with a least one response with submitted status will be updated from pending to completed.