config: add app.kubernetes.io/component label (#794)

* config: add `app.kubernetes.io/component` label

following the best practices when it comes to labelling objects (see
[1]), by making use of the recommended `app.kubernetes.io/component`,
we're able to clearly identify those objects that are part of
cartographer (useful for any tool that might want to do some form of
matching against anything cartographer-related, e.g., getting rid of all
of them based on matching on such label).

the approach I took here is to make use of ytt overlays in order to add
the label to all components _except_ the Namespace.

[1]: https://kubernetes.io/docs/concepts/overview/working-with-objects/common-labels/

Co-authored-by: Scott Andrews <andrewssc@vmware.com>
Co-authored-by: Emily Johnson <51918476+emmjohnson@users.noreply.github.com>

hack/overlays/component-labels.yaml

@@ -0,0 +1,23 @@
+# Copyright 2021 VMware
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+#@ load("@ytt:overlay", "overlay")
+
+#@overlay/match by=overlay.not_op(overlay.subset({"kind":"Namespace"})),expects="1+"
+---
+metadata:
+  #@overlay/match missing_ok=True
+  labels:
+    #@overlay/match missing_ok=True
+    app.kubernetes.io/component: cartographer

hack/release.sh

@@ -74,6 +74,7 @@ generate_release() {
         mkdir -p ./release
         ytt --ignore-unknown-comments -f ./config \
                 -f ./hack/overlays/webhook-configuration.yaml \
+                -f ./hack/overlays/component-labels.yaml \
                 --data-value version=$RELEASE_VERSION |
                 KO_DOCKER_REPO=$REGISTRY ko resolve -B -f- > \
                         ./release/cartographer.yaml