fix: fix and improve alembic migrations

[rivamarco]

In this PR:

• better handling of public schema due to Alembic behavior when using in default schema Alembic drop and create foreignkey on every migrate without any changes sqlalchemy/alembic#1351
• removed Unique constraint when field is also Primary Key due to a PostgreSQL behavior that lead Alembic to create constraint in subsequent migration Primary + unique constraint on same migration sqlalchemy/alembic#1494
• Use of naming conventions to avoid strange issues in subsequent migrations Unique constraint missing name/duplicated create_unique/drop_constraint sqlalchemy/alembic#1532 https://alembic.sqlalchemy.org/en/latest/naming.html

NB: old migrations are not usable anymore so they are deleted and replaced by this new one