feat: publish slack release testing status

[jake-perkins]

Description

This PR introduces an automated workflow that will periodically post the slack notification to the release slack channels of the testing/signoff status for the upcoming releases

Related issues

https://github.com/MetaMask/MetaMask-planning/issues/3647

Manual testing steps

CI/CD Testing
https://github.com/MetaMask/metamask-mobile/actions/runs/13295128229/job/37125160946 Sample CI Run
Sample Slack Post - https://consensys.slack.com/archives/C08BYUWAY59/p1739395363232389

Screenshots/Recordings

N/A - CI/CD Only

Pre-merge author checklist

• I’ve followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[sethkfman]

LGTM

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud