code: @NonNull
      public SourceParams setUsage(@NonNull @Source.Usage String usage) {
          mUsage = usage;
          return this;
      }
docs: Sets a usage value on the parameters. Used for Alipay, and should be
  either "single_use" or "reusable". Not setting this value defaults
  to "single_use".
  
  @param usage either "single_use" or "reusable"
  @return {@code this} for chaining purposes