Add milestone backport verification script and GitHub Action

[offtherailz]

Summary

Add a Python automation script (utility/automation/check_milestone.py) and a companion GitHub Actions workflow to verify that all issues assigned to a milestone have been correctly backported to the corresponding release branch.

Motivation

During release preparation, it is easy to miss a backport PR for a fix that was merged on master but not carried over to the stable branch (e.g. 2026.01.xx). Manual checking across many issues is time-consuming and error-prone. This tool automates the entire cross-check.

What was added

utility/automation/check_milestone.py

A standalone Python script (requires only requests) that:

1. Resolves the milestone by title (e.g. 2026.01.01) to its numeric GitHub API id, with full pagination support.
2. Fetches all issues in the milestone, excluding PR entries returned by the GitHub API.
3. Determines the branch-cut date by querying the merge-base commit between the main branch and the target branch. Issues whose main-branch PR was merged before the branch was cut are already included in the release branch and require no backport — they are marked ✅ automatically.
4. Classifies each issue with two Search API calls (one per branch) and assigns a status:

Icon	Status	Meaning
✅	OK	Backport merged, or merged before branch cut
⚠️	Missing backport	Merged on main, no backport PR found
📥	In progress	Merged on main, backport PR open
🏗️	In progress	Main PR still open
❓	No PR	No PR found anywhere (release tasks, manual items)

5. Prints a structured report with a per-issue row and a final summary bucketed by status.
6. Exits with code 1 only when confirmed missing backports are found, so it integrates cleanly in CI.

Rate-limit handling:

• Configurable sleep interval between Search API calls (2.5 s authenticated / 7 s unauthenticated).
• Exponential back-off with up to 5 retries on 403/429 responses, honouring the Retry-After header.

Configuration via CLI args or environment variables:

CLI arg	Env var	Default
--token	GITHUB_TOKEN	(empty)
--repo	REPO	geosolutions-it/MapStore2
--milestone	MILESTONE_TITLE	2026.01.01
--main-branch	MAIN_BRANCH	master
--branch	TARGET_BRANCH	2026.01.xx

.github/workflows/check_milestone.yml

A workflow_dispatch GitHub Actions workflow that runs the script on demand with inputs for milestone title, target branch, and main branch. Uses the built-in GITHUB_TOKEN — no additional secrets required.

Usage

Locally:

python utility/automation/check_milestone.py \
    --token ghp_... \
    --milestone 2026.01.01 \
    --branch 2026.01.xx

GitHub Actions: trigger manually from the Actions tab, filling in the two required inputs.