[CI] Add Kubernetes memory limits to docker_image_build_otel job (#49233)

### What does this PR do?

Adds `KUBERNETES_MEMORY_REQUEST` and `KUBERNETES_MEMORY_LIMIT` (32Gi) to
the `docker_image_build_otel` CI job, which was the only OTel
integration test job without Kubernetes memory limits.

### Motivation

The `docker_image_build_otel` job has a **~12% flaky failure rate** on
`main`, caused by OOM kills during `go mod download` of 40+ OTel modules
inside a Docker-in-Docker build (see [Slack
thread](https://dd.slack.com/archives/CR5TV8QBY/p1775901945411339)).

**Root cause analysis** ([posted in
thread](https://dd.slack.com/archives/CR5TV8QBY/p1775979407970919?thread_ts=1775901945.411339&cid=CR5TV8QBY)):

- Datadog CI data shows **64 failures / 469 successes over 7 days**
(~12%), with failures pre-dating the initially suspected PR #48777 (one
failure on Apr 9, a day before the PR merged)
- **60%** of failures are Kubernetes pod scheduling failures
(insufficient memory, unmatched node affinity)
- **25%** are silent process kills (exit code 255) during `go mod
download` — classic OOM pattern
- The two sibling OTel jobs already have memory limits:
  - `integration_tests_otel`: 16Gi
  - `datadog_otel_components_ocb_build`: 32Gi + 16 CPU
- `docker_image_build_otel` had **none**, relying on runner defaults

Setting REQUEST = LIMIT = 32Gi gives the pod a Guaranteed QoS class in
Kubernetes, matching the OCB build job which performs the same workload
(OCB generation + Go compilation).

### Describe how you validated your changes

- The YAML structure matches the existing pattern used by all other jobs
in this file
- The 32Gi value matches `datadog_otel_components_ocb_build` which does
the same work
- Validation will come from observing the failure rate drop after merge

### Additional Notes

The `.ddot_byoc_oci_build_test` template and
`ddot_byoc_binary_build_test_ubuntu2004` job in the same file also lack
memory limits and perform similar Docker builds. They may benefit from
the same treatment as a follow-up.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: L3n41c

.gitlab/test/integration_test/otel.yml

@@ -24,6 +24,9 @@ docker_image_build_otel:
   image: registry.ddbuild.io/ci/datadog-agent-buildimages/docker_x64$CI_IMAGE_DOCKER_X64_SUFFIX:$CI_IMAGE_DOCKER_X64
   needs: ["integration_tests_otel"]
   tags: ["docker-in-docker:amd64"]
+  variables:
+    KUBERNETES_MEMORY_REQUEST: 32Gi
+    KUBERNETES_MEMORY_LIMIT: 32Gi
   before_script:
     - mkdir -p /tmp/otel-ci
     - cp comp/otelcol/collector-contrib/impl/manifest.yaml /tmp/otel-ci/