Datadog integration for Gitlab pipelines v1

What does this MR do?

Add integration with Datadog to enable pipeline and job service hooks as discussed in #270123

Screenshots (strongly suggested)

Integrations list:

Integration form:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done