Use code-generator to generate clientset/informer/lister (#1492)

To reduce maintenance effort and avoid writing duplicate informer code,
use code-generator to generate clientset/informer/lister code.

pkg/apis/README.md

@@ -0,0 +1,18 @@
+# Fission CRD generation
+
+* Clone https://github.com/fission/code-generator to generate fission CRD object deepcopy and client methods.
+* MUST run code-generator in the fission root directory.
+
+``` bash
+$ cd $GOPATH/src/github.com/fission/fission/
+$ $GOPATH/src/k8s.io/code-generator/generate-groups.sh \
+    all \
+    github.com/fission/fission/pkg/apis/genclient/v1 \
+    github.com/fission/fission/pkg/apis \
+    fission.io:v1 \
+    --go-header-file $GOPATH/src/github.com/fission/fission/pkg/apis/boilerplate.txt
+```
+
+# Reference
+
+* https://blog.openshift.com/kubernetes-deep-dive-code-generation-customresources/