db diff fails with containers stopped

[nianiam]

Describe the bug
Until recently (#3600 and #3747), you had to stop your local containers in order to run db diff -f <file_name>. The DX improvement not having to stop the containers is a huge win (thanks!), but now if you stop the containers then the command fails. This is confusing given the documentation still states you need to stop the containers.

To Reproduce
Steps to reproduce the behavior:

1. Install CLI v2.28.2 or above
2. supabase stop
3. supabase db diff -f test

failed to connect to postgres: failed to connect to `host=127.0.0.1 user=postgres database=postgres`: dial error (dial tcp 127.0.0.1:54322: connect: connection refused)

Expected behavior
db diff should continue to run against the declarative schema whilst containers are stopped OR update the docs to reflect this change.