Prepare work for well known types (#2973)

## Changes
Prepare work for well known types. 

Well Known Types have a different wire format than the desired SDK type.
We are introducing dedicated types in the genkit model. This PR updates
the CLI to recognise these new types, but continue generating the fields
with the same type.

A follow-up PR will be created to include full support.


## Why
Generated CLI with an empty diff.

## Tests
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Author: hectorcast-db

.codegen/service.go.tmpl

@@ -128,7 +128,7 @@ func new{{.PascalName}}() *cobra.Command {
 
 	var {{.CamelName}}Req {{.Service.Package.Name}}.{{.Request.PascalName}}
 	{{- if .RequestBodyField }}
-	{{.CamelName}}Req.{{.RequestBodyField.PascalName}} = {{ if .RequestBodyField.IsOptionalObject }}&{{end}}{{.Service.Package.Name}}.{{.RequestBodyField.Entity.PascalName}}{}
+	{{.CamelName}}Req.{{.RequestBodyField.PascalName}} = {{ if .RequestBodyField.IsOptionalObjectPb }}&{{end}}{{.Service.Package.Name}}.{{.RequestBodyField.Entity.PascalName}}{}
 	{{- end }}
 	{{- if $canUseJson}}
 	var {{.CamelName}}Json flags.JsonFlag
@@ -390,6 +390,9 @@ func new{{.PascalName}}() *cobra.Command {
 
 {{- define "arg-type" -}}
 	{{- if .IsString}}StringVar
+	{{- else if .IsTimestamp}}StringVar{{/* TODO: add support for well known types */}}
+	{{- else if .IsDuration}}StringVar{{/* TODO: add support for well known types */}}
+	{{- else if .IsFieldMask}}StringVar{{/* TODO: add support for well known types */}}
 	{{- else if .IsBool}}BoolVar
 	{{- else if .IsInt64}}Int64Var
 	{{- else if .IsFloat64}}Float64Var
@@ -409,7 +412,7 @@ func new{{.PascalName}}() *cobra.Command {
 	{{- if $optionalIfJsonIsUsed  }}
 	if !cmd.Flags().Changed("json") {
 	{{- end }}
-	{{if not $field.Entity.IsString -}}
+	{{if and (not $field.Entity.IsString) (not $field.Entity.IsFieldMask) (not $field.Entity.IsTimestamp) (not $field.Entity.IsDuration) -}} {{/* TODO: add support for well known types */}}
 	_, err = fmt.Sscan(args[{{$arg}}], &{{- template "request-body-obj" (dict "Method" $method "Field" $field)}})
 	if err != nil {
 		return fmt.Errorf("invalid {{$field.ConstantName}}: %s", args[{{$arg}}])