CLOUDP-295785 - remove title from changelog file generator

[MaciejKaras]

Summary

Based on discussions we had here we have decided to drop title from changelog files frontmatter. This gives false assumption that it will be included in the final Release Notes, which is not the case. Additionally title didn't have any meaningful usage. Now it will be added as initial contents of the file and dropped from frontmatter.

Proof of Work

Creating a changelog after updating:

(venv) ➜  mongodb-kubernetes git:(maciejk/ar-changelog-remove-title) python3 -m scripts.release.create_changelog -k feature "Test something that is very long title about some feature" -e
Created changelog entry at: /Users/maciej.karas/mongodb/mongodb-kubernetes/changelog/20250915_feature_test_something_that_is_very_long_title_about_some.md

(venv) ➜  mongodb-kubernetes git:(maciejk/ar-changelog-remove-title) ✗ cat changelog/20250915_feature_test_something_that_is_very_long_title_about_some.md
---
kind: feature
date: 2025-09-15
---

* Test something that is very long title about some feature

(venv) ➜  mongodb-kubernetes git:(maciejk/ar-changelog-remove-title) python3 -m scripts.release.release_notes --initial-version 1.2.0
# MCK 1.4.0 Release Notes

## New Features

* Some feature that is properly described with full context

Checklist

• Have you linked a jira ticket and/or is the ticket in the title?
• Have you checked whether your jira ticket required DOCSP changes?
• Have you added changelog file?
  • use skip-changelog label if not needed
  • refer to Changelog files and Release Notes section in CONTRIBUTING.md for more details

[github-actions]

⚠️ (this preview might not be accurate if the PR is not rebased on current master branch)

MCK 1.3.1 Release Notes

[vinilage]

LGTM