Pass MR vars to downstream pipelines via `scripts/trigger-build`

What does this MR do?

Adds 2 env vars to those passed to downstream pipelines when they're triggered by scripts/trigger-build

• CI_MERGE_REQUEST_PROJECT_ID as TOP_UPSTREAM_MERGE_REQUEST_PROJECT_ID
• CI_MERGE_REQUEST_IID as TOP_UPSTREAM_MERGE_REQUEST_IID

Part of #201829 (closed)

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