Send main build metrics (#447)

*Issue #, if available:*

*Description of changes:*
Emit a failure metric if main build fails. Since this workflow is
triggered with pushes to main or a release branch, we want to be
notified if there is a failure with the build process or e2e tests.

Tested by temporarily adding an `on: push:` trigger to my own branch in
this repo and testing the updated workflow. Verified that failure metric
was successfully published to cloudwatch.

https://github.com/aws-observability/aws-otel-js-instrumentation/actions/runs/16764243839

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choice.

Author: ezhang6811

.github/workflows/main-build.yml

@@ -109,3 +109,23 @@ jobs:
     with:
       staging-wheel-name: ${{ needs.build.outputs.staging_wheel_file }}
       adot-image-name: ${{ needs.build.outputs.staging_registry }}/aws-observability/adot-autoinstrumentation-python-staging:${{ needs.build.outputs.python_image_tag }}
+
+  publish-main-build-status:
+    name: "Publish Main Build Status"
+    needs: [ build, application-signals-e2e-test ]
+    runs-on: ubuntu-latest
+    if: always()
+    steps:
+      - name: Configure AWS Credentials for emitting metrics
+        uses: aws-actions/configure-aws-credentials@v4
+        with:
+          role-to-assume: ${{ secrets.MONITORING_ROLE_ARN }}
+          aws-region: ${{ env.AWS_DEFAULT_REGION }}
+
+      - name: Publish main build status
+        run: |
+          value="${{ needs.build.result == 'success' && needs.application-signals-e2e-test.result == 'success' && '0.0' || '1.0'}}"
+          aws cloudwatch put-metric-data --namespace 'ADOT/GitHubActions' \
+            --metric-name Failure \
+            --dimensions repository=${{ github.repository }},branch=${{ github.ref_name }},workflow=main_build \
+            --value $value