Add "name_position" option to name_new/firstupdate/update

[JeremyRand]

Is your feature request related to a problem? Please describe.

When the send RPC method inserts an output that the user did not explicitly ask for (i.e. the change output), the output's position is configurable via the change_position option. The name RPC methods also insert such an output (i.e. the name output), but the position is not configurable similarly, which is unfortunate.

Describe the solution you'd like

Add a name_position field to the options parameter of the name RPC methods, which influences the name output similarly to how the change_position field in send influences the change output, so that name transactions have feature parity with currency transactions.

Describe alternatives you've considered

N/A.

Additional context

N/A.