chore: add CHANGELOG.md check workflow on PRs

[joaodordio]

📝 Summary

This should be a 150 characters summary of the changes on this PR

Add a CI check that fails PRs when CHANGELOG.md is not updated, unless the description declares "No customer facing changes".

🎟️ Jira Ticket: N/A — internal CI tooling

📖 Description

Please provide a description of what this pull request does.

Adds .github/workflows/changelog-check, a workflow that runs on every PR (opened, edited, synchronize, reopened). The check passes when either CHANGELOG.md is among the PR's changed files, or the PR description contains the phrase "No customer facing changes". Otherwise it fails with a message explaining how to resolve it.

Also adds a 🧾 Changelog section to the PR template documenting the opt-out phrase. Read-only token, no checkout, fork-safe, and not restricted by base branch so it covers every PR.

🧪 How to test?

How to test the changes added?

• Open a PR that does not touch CHANGELOG.md and omits the opt-out phrase → the check fails.
• Edit the description to add "No customer facing changes" (or update CHANGELOG.md) → the check passes on the next run without a new commit.

🧾 Changelog

Add an entry to CHANGELOG.md. If this PR has no customer facing changes, write "No customer facing changes" here to skip the changelog check.

No customer facing changes

📹 Loom recording if applicable

N/A

🐞 Github Issues solved

N/A

📚 Docs PR if applicable

N/A