Add a primitive list operation

This needs to be done better for FM-7700, but is required now for getting the schema for the context when retrieving facts.

Author: DavidS

lib/puppet/resource_api/transport.rb

@@ -18,6 +18,12 @@ def register(schema)
   end
   module_function :register # rubocop:disable Style/AccessModifierDeclarations
 
+  # retrieve a Hash of transport schemas, keyed by their name.
+  def list
+    @transports || {}
+  end
+  module_function :list # rubocop:disable Style/AccessModifierDeclarations
+
   def connect(name, connection_info)
     validate(name, connection_info)
     require "puppet/transport/#{name}"