When DB credentials change (derived from matrix_synapse_macaroon_secret_key),
a running Synapse container may fail to connect to its database and stop
serving requests. This causes register_new_matrix_user to fail with
"Connection refused" when the matrix-user-creator role tries to register users.

This extends the retry logic from 44b43a51b (which handled HMAC failures)
to also handle Connection refused errors: restart Synapse (picking up the
new config with updated credentials), wait for it to start, and retry.

Caused by c21a80d232

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>