[api docs] Stabilize build (#205432)

The API docs build times have become unstable over the last few months,
ranging from 45 to 80 minutes before timing out:
https://buildkite.com/elastic/kibana-api-docs-daily/builds?state=failed.

When the API docs build times out in the on-merge pipeline, or takes
longer than a pull request build, pull requests based on it will also
fail due to missing baseline metrics. Testing at
https://buildkite.com/elastic/kibana-pull-request/builds/263821 and
https://buildkite.com/elastic/kibana-pull-request/builds/263838
indicates consistency and time improvements with more memory.

This updates the machine type from n2-standard-4 to n2-highmem-4 and
allocates 24gb to the node process.

.buildkite/pipelines/build_api_docs.yml

@@ -18,7 +18,7 @@ steps:
       image: family/kibana-ubuntu-2004
       imageProject: elastic-images-prod
       provider: gcp
-      machineType: n2-standard-4
+      machineType: n2-highmem-4
       preemptible: true
     key: build_api_docs
     timeout_in_minutes: 50

.buildkite/pipelines/on_merge.yml

@@ -133,7 +133,7 @@ steps:
       image: family/kibana-ubuntu-2004
       imageProject: elastic-images-prod
       provider: gcp
-      machineType: n2-standard-4
+      machineType: n2-highmem-4
       preemptible: true
       diskSizeGb: 75
     timeout_in_minutes: 80

.buildkite/pipelines/pull_request/base.yml

@@ -136,7 +136,7 @@ steps:
   - command: .buildkite/scripts/steps/api_docs/build_api_docs.sh
     label: 'Build API Docs'
     agents:
-      machineType: n2-standard-4
+      machineType: n2-highmem-4
       preemptible: true
       diskSizeGb: 75
     key: build_api_docs

.buildkite/scripts/steps/api_docs/build_api_docs.sh

@@ -5,7 +5,7 @@ set -euo pipefail
 .buildkite/scripts/bootstrap.sh
 
 echo "--- Build API Docs"
-node --max-old-space-size=12000 scripts/build_api_docs
+node --max-old-space-size=24000 scripts/build_api_docs
 
 if [[ "${PUBLISH_API_DOCS_CHANGES:-}" == "true" ]]; then
   echo "--- Store API Docs changes in Buildkite"

.buildkite/scripts/steps/checks/baseline_plugin_public_api_docs.sh

@@ -5,4 +5,4 @@ set -euo pipefail
 source .buildkite/scripts/common/util.sh
 
 echo --- Building api docs
-node --max-old-space-size=12000 scripts/build_api_docs
+node --max-old-space-size=24000 scripts/build_api_docs

.buildkite/scripts/steps/on_merge_api_docs.sh

@@ -7,4 +7,4 @@ export DISABLE_BOOTSTRAP_VALIDATION=true
 .buildkite/scripts/bootstrap.sh
 
 echo "--- Build API Docs"
-node --max-old-space-size=12000 scripts/build_api_docs
+node --max-old-space-size=24000 scripts/build_api_docs