add documentation about downgrading ambiguous walk

[lolopinto]

should actually fix the issue if possible ala https://github.com/lolopinto/ent/issues/915 but adding documentation to https://ent.dev/docs/advanced-topics/cli#downgrade helpful

[lolopinto]

steps after error

1. docker-compose -f docker-compose.dev.yml run --rm app tsent alembic heads to see dependencies

 description
    
    Revision ID: {rev1}
    Revises: {prev1}, {prev2}
    Create Date: {date}

2. docker-compose -f docker-compose.dev.yml run --rm app tsent downgrade rev1@rev2 to downgrade