Move ChatOps to Core
What does this MR do?
Copies all relevant parts of ChatOps from EE.
Tested this locally using a newly setup Slack workspace and this guide

What are the relevant issue numbers?
Does this MR meet the acceptance criteria?
- Changelog entry added, if necessary
- Documentation created/updated via this MR
- Documentation reviewed by technical writer or follow-up review issue created
- Tests added for this feature/bug
- [-] Tested in all supported browsers
- Conforms to the code review guidelines
- Conforms to the merge request performance guidelines
- Conforms to the style guides
- Conforms to the database guides
- [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
- [-] Security reports checked/validated by reviewer