Feature: Pre/Post release for application groups

[Himansri21]

🔖 Feature description

Application Groups support triggering pre-deployment stages across multiple applications via bulk trigger, but each pre-deployment stage is configured and executed independently per-application. There is no native way to define a single hook that runs:

• Once, before any application in the group deploys (a true group-level pre-release step), or
• Once, after all applications in the group have finished deploying (a true group-level post-release step)

🎤 Pitch / Usecases

Example use cases:

1. Database migrations: Triggering schema migrations via a pre-deploy stage on each application independently risks concurrent/duplicate execution against the shared database, since multiple pre-deploy stages fire in parallel across the group. A single group-level pre-release hook would ensure migrations run exactly once, before any pod in the group is deployed.
2. Post-deploy data backfill: Some tasks (e.g., data backfills) should only run after every application in the group has successfully deployed. Today, this requires manually polling/monitoring deployment status across all N services in the group, since there's no synchronization mechanism at the post-deploy stage. A group-level post-release hook would let this be defined once, rather than orchestrated manually per-application.

🔄️ Alternative

create a separate custom job in the Devtron Jobs section that runs independently of the individual application pipelines, and is manually triggered (or scripted to poll deployment status) before/after the Application Group deployment to simulate the pre/post-release behavior.

👀 Have you spent some time to check if this issue has been raised before?

• I checked and didn't find similar issue

🏢 Have you read the Code of Conduct?

• I have read the Code of Conduct