dev/sg: support update custom compose file

Created by: michaellzc

use case:

I want to be able to use sg to update non docker-compose.yaml docker-compose files. For example, for MI, I can use sg to pin unreleased images

Test plan

Create

curl -o docker-compose.insiders.yaml https://raw.githubusercontent.com/sourcegraph/deploy-sourcegraph-docker/3.41.0/docker-compose/docker-compose.yaml

sg ops update-images -kind compose docker-compose.insiders.yaml

the file should be updated to the latest unreleae images