feat: add a GitHub Action to notify a TAE on Slack when a review tag is added to PR

[sahil-sumo]

Purpose of this pull request

Sets up the GitHub Actions workflow that automatically assigns a TAE reviewer to documentation PRs on a round-robin basis and notifies the assignee and labeler in Slack.

Select the type of change

• Minor Changes - Typos, formatting, slight revisions
• Update Content - Revisions, updating sections
• New Content - New features, sections, pages, tutorials
• Site and Tools - .clabot, version updates, maintenance, dependencies, new packages for the site (Docusaurus, Gatsby, React, etc.)

Ticket (if applicable)

Jira Ticket

NOTE: DO NOT MERGE until rest of the prerequisites mentioned in the Jira Epic are completed

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[kimsauce]

Hi @sahil-sumo , I've just added the two CS_REVIEWER_SLACK_ secrets on the back end. Can you test & confirm the workflow now works as expected?

[sahil-sumo]

Hi @sahil-sumo , I've just added the two CS_REVIEWER_SLACK_ secrets on the back end. Can you test & confirm the workflow now works as expected?

Thank you @kimsauce , I'm waiting on Mark to complete the other pre-requisite tasks mentioned in the Jira Epic before I can test this out.