doc/dev: dont reload prometheus with sg override

Created by: bobheadxi

As I was hacking on https://github.com/sourcegraph/sourcegraph/pull/31518 I realized... the monitoring generator might have been reloading the remote prometheus instance I was connected to 😰 This updates the sg override config snippet to disable prometheus reload.

Test plan

With the provided config snippet:

sg start monitoring

Should no longer see Prometheus reload messages 😁