[CHORE] Add workflow for Github issue notifications to Slack

[sbarrio]

What does this PR do?

This PR introduces an automated GitHub issue handler that fetches issue details and posts notifications to Slack. This helps streamline issue triage and provides immediate visibility when new issues are opened. See this doc (internal) for more.

For more information on the inner workings of this check the original PR by @mariedm on the dd-sdk-ios repository.

Motivation

When this action is enabled, whenever we get a new issues it will parse it, analyze and send a summary to our internal Slack channels.

Additional Notes

This PR introduces the GH action as a manually triggered workflow first. Once it has been properly tested a subsequent PR will enable it to run automatically when a new issues is opened.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)
• If this PR is auto-generated, please make sure also to manually update the code related to the change

[sbarrio]

Automatic runs of this action are initially disabled until proper testing has been performed.