ci(actions): Add slapr workflow for Slack emoji PR updates

[chouetz]

What does this PR do?

Adds a new GitHub Actions workflow (.github/workflows/slapr.yml) that integrates slapr to post Slack emoji updates on PRs based on review status.

The workflow:

• Triggers on pull_request_review (submitted) and pull_request (closed) events
• Uses dd-octo-sts to obtain a scoped GitHub token with contents:read, pull_requests:read, and members:read permissions
• Runs slapr with the github_slack_map.yaml review map to resolve team-to-channel mappings

Motivation

Automate Slack notifications for PR review activity, giving teams visibility into review progress directly in their Slack channels.

Describe how you validated your changes

• Verified the dd-octo-sts policy (self.slapr.read-members) is set up in a companion PR: ci(chainguard): Add dd-octo-sts policy for slapr workflow #47838
• The slapr action reference points to nicolas.schweitzer/review-map branch (will be updated to a release tag before merging)

Additional Notes

• Dependency: Requires the dd-octo-sts policy from ci(chainguard): Add dd-octo-sts policy for slapr workflow #47838 and the YAML format change from refactor(notifications): Change GitHub-Slack map YAML format to dict entries #47782
• Secrets/vars needed: SLAPR_SLACK_API_TOKEN secret, SLACK_CHANNEL_ID and SLAPR_BOT_USER_ID repository variables
• The slapr action ref (nicolas.schweitzer/review-map) is a development branch and should be pinned to a release before this PR is merged

[agent-platform-auto-pr]

Files inventory check summary

File checks results against ancestor 2c465803:

Results for datadog-agent_7.78.0~devel.git.590.5168faf.pipeline.102518963-1_amd64.deb:

No change detected