chore(serverless): add more upstream variables for benchmark notification (#8811)

### What does this PR do?
Adds a couple variables for downstream Serverless benchmark job.

### Motivation
Provide users with meaningful links for PRs failing on the main branch.
<img width="693" alt="Screenshot 2024-03-29 at 3 55 35 PM"
src="https://github.com/DataDog/dd-trace-js/assets/30836115/e43a1167-65b6-411d-bfc3-8e4fb0f350d3">

## Checklist

- [x] Change(s) are motivated and described in the PR description
- [x] Testing strategy is described if automated tests are not included
in the PR
- [x] Risks are described (performance impact, potential for breakage,
maintainability)
- [x] Change is maintainable (easy to change, telemetry, documentation)
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed or label `changelog/no-changelog` is set
- [x] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/))
- [x] Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))
- [x] If this PR changes the public interface, I've notified
`@DataDog/apm-tees`.
- [x] If change touches code that signs or publishes builds or packages,
or handles credentials of any kind, I've requested a review from
`@DataDog/security-design-and-guidance`.

## Reviewer Checklist

- [x] Title is accurate
- [x] All changes are related to the pull request's stated goal
- [x] Description motivates each change
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- [x] Testing strategy adequately addresses listed risks
- [x] Change is maintainable (easy to change, telemetry, documentation)
- [x] Release note makes sense to a user of the library
- [x] Author has acknowledged and discussed the performance implications
of this PR as reported in the benchmarks PR comment
- [x] Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Author: duncanista

.gitlab/benchmarks.yml

@@ -136,6 +136,10 @@ benchmark-serverless-trigger:
     strategy: depend
   allow_failure: true
   variables:
+    variables:
+    UPSTREAM_PIPELINE_ID: $CI_PIPELINE_ID
+    UPSTREAM_PROJECT_URL: $CI_PROJECT_URL
     UPSTREAM_COMMIT_BRANCH: $CI_COMMIT_BRANCH
     UPSTREAM_COMMIT_AUTHOR: $CI_COMMIT_AUTHOR
     UPSTREAM_PROJECT_NAME: $CI_PROJECT_NAME
+    UPSTREAM_MERGE_REQUEST_SOURCE_BRANCH_NAME: $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME