Enable crd variables and controller functions and hooks within hook templates

[kumargauravsharma]

Issue #, aws-controllers-k8s/community#838

Description of changes:
This PR enables support for crd variables and controller functions and hooks within hook templates.
The hook templates insides the service controllers can be similar to the templates that are inside code-generator.

For example, following hook template refers .CRD variable, invokes controller function GoCodeSetCreateOutput and has its own extension hook sdk_addon_set_output_post_populate:
and it can be used as hook inside generator.yaml for a resource:

{{ $outputShape := .CRD.GetOutputShape .CRD.Ops.Create }}
// This method copies the data from given {{ $outputShape.ShapeName }} by populating it
// into copy of supplied resource and returns that.
func (rm *resourceManager) set{{ $outputShape.ShapeName }}Output (
    r *resource,
    obj *svcsdk.{{ $outputShape.ShapeName }},
) (*resource, error) {
	if obj == nil ||
		r == nil ||
		r.ko == nil {
		return nil, nil
	}
	resp := &svcsdk.{{ .CRD.Ops.Create.OutputRef.Shape.ShapeName }}{ {{ $outputShape.ShapeName }}:obj }
	// Merge in the information we read from the API call above to the copy of
    // the original Kubernetes object we passed to the function
    ko := r.ko.DeepCopy()
{{ $createCode := GoCodeSetCreateOutput .CRD "resp" "ko" 1 true }}
{{ $createCode }}
	rm.setStatusDefaults(ko)
{{- if $hookCode := Hook .CRD "sdk_addon_set_output_post_populate" }}
{{ $hookCode }}
{{- end }}
    return &resource{ko}, nil
}

Testing:
make test passed for code-generator

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

[kumargauravsharma]

Related PR: aws-controllers-k8s/elasticache-controller#36 where dynamic hook template is used to auto generate reusable setOutput method.

[a-hilaly]

Nice!
/approve

[kumargauravsharma]

Could this PR be merged?

[jaypipes]

👍

[jaypipes]

/lgtm

[ack-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: A-Hilaly, jaypipes, kumargauravsharma

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[a-hilaly]

/ok-to-test