update deploy-sourcegraph release steps
Created by: bobheadxi
for https://github.com/sourcegraph/sourcegraph/issues/13122
Proposes some changes to the release steps to make branch cuts first, and target renovate release updates to specific branches rather than master
. Image updates for release now happen via GitHub Actions with a manual trigger.
This is tied to https://github.com/sourcegraph/deploy-sourcegraph/pull/845, which changes the deploy-sourcegraph
model to track insiders
instead of releases on master