Execute gstg-cny QA from the coordinated pipeline

Starting on gitlab-org/gitlab#340639 (closed), gstg-cny triggers QA jobs through the deployer pipeline. Following the same setup as gstg and gprd-cny, it'd be helpful for &608 (closed) to trigger gstg-cny QA from the coordinated pipeline

Proposal

Trigger gstg-cny QA from the coordinated pipeline. We might need to create another stage and use bridge-jobs to trigger downstream pipelines.

Considerations:

• On auto-deploys, QA should be triggered from the coordinated pipeline.
• When executing a deployment via ChatOps, QA should be triggered from deployer.
• Results from tests should be posted in #qa-staging

Plan

• Modify deployer CI configuration to skip QA jobs when triggered by release-tools - https://ops.gitlab.net/gitlab-com/gl-infra/deployer/-/merge_requests/486
• Add QA bridge-jobs for gstg-cny on release-tools - gitlab-org/release-tools!1826 (merged)