Add sdk addon hook (#94)

Issue #, if available:

Ability for service controllers to add code (additional functions, variables etc as needed) to sdk.go file using hooks as extension mechanism.

Description of changes:

This PR adds `sdk_addon` hook to `sdk.go.tpl`. Using this hook, service controllers can append code to a custom resource's `sdk.go` file. It will help in placing reusable code/functions which are generated dynamically using hook templates.

Following PR contains changes showcasing how this facility helps service controllers auto generate reusable code: aws-controllers-k8s/elasticache-controller#36

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Author: kumargauravsharma

pkg/generate/ack/hook.go

@@ -56,6 +56,7 @@ code paths:
 * sdk_get_attributes_post_set_output
 * sdk_create_post_set_output
 * sdk_update_post_set_output
+* sdk_file_end
 * delta_pre_compare
 * delta_post_compare
 
@@ -91,6 +92,10 @@ is merged with the copy of the original Kubernetes object. These hooks will
 have access to the updated Kubernetes object `ko`, the response of the API call
 (and the original Kubernetes CR object if its sdkUpdate)
 
+The "sdk_file_end" is a generic hook point that occurs outside the scope of any
+specific AWSResourceManager method and can be used to place commonly-generated
+code inside the sdk.go file
+
 The "delta_pre_compare" hooks are called BEFORE the generated code that
 compares two resources.
 

templates/pkg/resource/sdk.go.tpl

@@ -362,3 +362,6 @@ func (rm *resourceManager) handleImmutableFieldsChangedCondition(
 	return &resource{ko}
 }
 {{- end }}
+{{- if $hookCode := Hook .CRD "sdk_file_end" }}
+{{ $hookCode }}
+{{- end }}