Enable minimal embedded status is alpha integration tests

In tektoncd/pipeline#5032, we added the logic
for setting embedded status when running end to end tests.

In this change, we set `embedded-status` to `"minimal"` so that we
can dogfood the feature alongside other alpha features. This also
allows us to run examples with `Matrix` which needs minimal embedded
status.

Author: jerop

prow/config.yaml

@@ -988,6 +988,8 @@ presubmits:
         env:
         - name: PIPELINE_FEATURE_GATE
           value: "alpha"
+        - name: EMBEDDED_STATUS_GATE
+          value: "minimal"
   - name: pull-tekton-pipeline-go-coverage
     labels:
       preset-github-token: "true"