Add a .diff target for k8s_deploy (#55)

Author: borg286

README.md

@@ -51,6 +51,8 @@ For example, let's look at the [example's k8s_deploy](./e2e/helloworld/BUILD.baz
 cd e2e
 bazel run //helloworld:mynamespace.show
 ```
+We can run `bazel run ///helloworld:mynamespace.diff` to see a difference from source to what is stored in kubernetes.
+
 When you run `bazel run ///helloworld:mynamespace.apply`, it applies this file into your personal (`{BUILD_USER}`) namespace. Viewing the rendered files with `.show` can be useful for debugging issues with invalid or misconfigured manifests.
 
 | Parameter                 | Default        | Description

skylib/k8s.bzl

@@ -223,6 +223,17 @@ def k8s_deploy(
             tags = tags,
             visibility = visibility,
         )
+        kubectl(
+            name = name + ".diff",
+            srcs = [name],
+            command = "diff",
+            cluster = cluster,
+            push = False,
+            user = user,
+            namespace = namespace,
+            tags = tags,
+            visibility = visibility,
+        )
         show(
             name = name + ".show",
             namespace = namespace,