feat: unify release announcements with per-repo webhook routing via repository secret

[gandalf-at-lerian]

🚀 Feature Request

Summary

Unify release announcement notifications within the release umbrella workflow, routing them to specific Slack/webhook channels per repository, with the webhook URL defined as a repository-level secret.

Motivation

Currently, release notifications are either hardcoded or not centrally managed across repositories. As the number of repos using shared release workflows grows, we need a scalable pattern where each repository controls its own notification target without touching the shared workflow code.

Proposed Solution

• Add an optional webhook_url input (or read from a repository secret, e.g. RELEASE_WEBHOOK_URL) to the release umbrella workflow
• When the secret/input is present, the workflow dispatches a POST to that webhook after a successful release
• The webhook payload should include: release tag, repo name, release URL, actor, and ref
• Each repository defines its own RELEASE_WEBHOOK_URL secret pointing to the desired channel (Slack, Discord, Teams, etc.)
• If the secret is absent, the step is skipped gracefully (no breaking change)

Acceptance Criteria

• Release umbrella workflow reads RELEASE_WEBHOOK_URL from repository secrets
• Webhook POST is triggered on successful release with a standard payload
• Step is skipped (non-fatal) when secret is not defined
• Documentation updated with setup instructions for consuming repositories
• At least one example payload documented

Example Secret Setup (consuming repo)

Settings → Secrets and variables → Actions → New repository secret
Name: RELEASE_WEBHOOK_URL
Value: https://hooks.slack.com/services/xxx/yyy/zzz

Payload (suggested)

{
  "repo": "LerianStudio/midaz",
  "tag": "v4.0.0",
  "release_url": "https://github.com/LerianStudio/midaz/releases/tag/v4.0.0",
  "actor": "github-actions[bot]",
  "ref": "refs/tags/v4.0.0"
}

Additional Context

This was surfaced from the #lerian-product-release channel where release notifications from multiple repos land without differentiation by target audience or channel.