feat: add --check flag to migrate:create on Postgres

[IiroP]

What

Add --check flag to migrate:create on Postgres adapter. When the flag is applied, the command only checks if migrations are needed without actually creating new migrations.

• If schema is up-to-date and migrations are not needed, the command exits with code 0.
• If new migrations are needed, the command prints "Schema changes detected, a new migration is needed" and exits with code 1.

Why

This is useful for creating CI checks. There has been discussion about this at least in #10978.

[IiroP]

At least most of the CI errors seem to be npm timeouts, could someone try running them again or is there something I should do?

[jhb-dev]

This is exactly what I needed as well. Thanks for the PR!