build: add Zuul check pipeline

This pipeline checks the extension with |web-ext lint|.

Change-Id: I3bce686ff33fcbd24c0857da17eccd12458ed2ec
diff --git a/roles/build-extension/defaults/main.yaml b/roles/build-extension/defaults/main.yaml
new file mode 100644
index 0000000..ba0ea42
--- /dev/null
+++ b/roles/build-extension/defaults/main.yaml
@@ -0,0 +1 @@
+make_target: chromium-stable