(PDK-1333) Add command_spec rake task

Introspects the populated Cri data structure to generate a JSON
specification of the PDK command structure for use in generating the
PowerShell cmdlets.

rakelib/command_spec.rake

@@ -0,0 +1,25 @@
+task :command_spec do
+  require 'pdk/cli'
+  require 'json'
+
+  base_command = PDK::CLI.instance_variable_get('@base_cmd')
+  result = describe_command(base_command)
+  puts JSON.pretty_generate(result)
+end
+
+def describe_command(cri_command)
+  {
+    'name'        => cri_command.name,
+    'aliases'     => cri_command.aliases.to_a,
+    'description' => cri_command.description,
+    'hidden'      => cri_command.hidden,
+    'summary'     => cri_command.summary,
+    'usage'       => cri_command.summary,
+    'options'     => cri_command.option_definitions.map { |r| describe_option(r) },
+    'subcommands' => cri_command.subcommands.map { |r| describe_command(r) },
+  }
+end
+
+def describe_option(cri_option)
+  cri_option.reject { |k, _| k == :block }
+end