Create the 'Mappings' table

[jennifer-bowser]

Description

• For our Storage Refactor epic, we are creating a new "Mappings" table. See our LucidChart and GitHub Discussion for more details on what the Mappings table should look like.

• As part of this ticket, we should update our src/anyvar/storage/postgres.py > create_schema method so that it can create the Mappings table.

  • Note: if we've already finished Issue #202 prior to this ticket, then this functionality may have moved. But we'll need to update this logic no matter where it lives

• We'll need to update our liftover logic to save variants and their liftover equivalents to this table, rather than using annotations

• We'll also need to update our logic for forward and reverse transcription and translation to utilize the mapping table