Generate doc comments on param types

[rbalicki2]

• For each field in the generated param_type files, if the field has a description, we should generate a description like:

export type Pet__PetPhraseCard__param = {
  id: string,
  /**
   * The pet's favorite phrase. If you spoke pet, you would hear them say it
   * all the time.
   */
  favorite_phrase: (string | null),
};