update error messages about missing tables in the database to say "run spicedb migrate"

[miparnisari]

Many users on Discord have reported this friction: 1, 2, 3, 4, to name a few.

To reproduce: If you update https://github.com/authzed/spicedb/blob/main/docker-compose.yaml to remove the migrate service, and then run docker-compose up --build, and then try to write a schema, you get this:

// http 500
{
  "code": 2,
  "message": "unable to list caveat: ERROR: relation \"caveat\" does not exist (SQLSTATE 42P01)",
  "details": []
}

which makes a very poor experience since it doesn't tell the operator how to fix it.

Let's update all the error messages of type relation X does not exist for every datastore to include please run spicedb datastore migrate.