Add manual diff tests for schema changes

[GAlexIHU]

Overview

Adds a new dagger function for running diff tests between the current HEAD (including uncommitted) and a provided baseRef. Example command:

dagger call --source .:default etoe diff --baseRef d1fc578d195e9d6961ac0bd7e1bb5e77ec279736

The only test written for now asserts that a given change doesn't result a database schema change via ent automigrate.

Currently this is not included in the CI but it would be reasonably easy to do so. The reason for that is that baseRef has to have tools/migrate present, which main does not have, only this branch.

Notes for reviewer

Later on it would be easy to generalize the setup process (currently its linked to this single usecase)