chore: Add PR notification

[jamesnrokt]

Instructions

1. PR target branch should be against development
2. PR title name should follow this format: https://github.com/mParticle/mparticle-workflows/blob/main/.github/workflows/pr-title-check.yml
3. PR branch prefix should follow this format: https://github.com/mParticle/mparticle-workflows/blob/main/.github/workflows/pr-branch-check-name.yml

Summary

• Add PR notification

Testing Plan

• N/A

Reference Issue (For mParticle employees only. Ignore if you are an outside contributor)

• N/A

[Copilot]

Pull Request Overview

Adds a new GitHub Actions job to notify a Google Chat channel whenever a pull request is opened (and not in draft state).

• Introduce a pr-notify job that runs after pr-check on non-draft PR open events.
• Configure the job to call an external workflow for sending a GChat notification using a stored webhook secret.

Comments suppressed due to low confidence (3)

.github/workflows/pull-request.yml:15

• Verify that the pr-check job is defined earlier in this workflow and the job key matches exactly, so the needs reference resolves correctly.

      - pr-check

.github/workflows/pull-request.yml:10

• [nitpick] Consider renaming the job key from pr-notify to notify-gchat (or similar) to match kebab-case conventions and align with the descriptive name field.

  pr-notify:

.github/workflows/pull-request.yml:19

• [nitpick] Add a short comment above this section to document the expected format and purpose of the GCHAT_PRS_WEBHOOK secret for better maintainability.

      gchat_webhook: ${{ secrets.GCHAT_PRS_WEBHOOK }}