[ci] Conditional storybook builds (#136219) (#137889)

* [ci] Conditional storybook builds

This moves storybook builds to run conditionally, either if there's a
storybook change or the `ci:build-storybooks` label is set.

These builds don't seem to be providing test coverage, and may not be utilized
in scenarios such as automated backports or unrelated changes.

* test regex

* formatting

* Revert "test regex"

This reverts commit dcef465414.

* fix revert

* move to spot instance

* fix merge

(cherry picked from commit 22b21645bb)

Co-authored-by: Jonathan Budzenski <jon@elastic.co>

.buildkite/pipelines/pull_request/base.yml

@@ -62,13 +62,6 @@ steps:
       queue: c2-8
     timeout_in_minutes: 60
 
-  - command: .buildkite/scripts/steps/storybooks/build_and_upload.sh
-    label: 'Build Storybooks'
-    agents:
-      queue: c2-4
-    key: storybooks
-    timeout_in_minutes: 60
-
   - command: .buildkite/scripts/steps/build_api_docs.sh
     label: 'Build API Docs'
     agents:

.buildkite/pipelines/pull_request/storybooks.yml

@@ -0,0 +1,7 @@
+steps:
+  - command: .buildkite/scripts/steps/storybooks/build_and_upload.sh
+    label: 'Build Storybooks'
+    agents:
+      queue: n2-4-spot
+    key: storybooks
+    timeout_in_minutes: 60

.buildkite/scripts/pipelines/pull_request/pipeline.ts

@@ -118,6 +118,13 @@ const uploadPipeline = (pipelineContent: string | object) => {
       pipeline.push(getPipeline('.buildkite/pipelines/pull_request/deploy_cloud.yml'));
     }
 
+    if (
+      (await doAnyChangesMatch([/.*stor(ies|y).*/])) ||
+      GITHUB_PR_LABELS.includes('ci:build-storybooks')
+    ) {
+      pipeline.push(getPipeline('.buildkite/pipelines/pull_request/storybooks.yml'));
+    }
+
     if (GITHUB_PR_LABELS.includes('ci:build-webpack-bundle-analyzer')) {
       pipeline.push(getPipeline('.buildkite/pipelines/pull_request/webpack_bundle_analyzer.yml'));
     }