Support output tree in ghhops-server

[sbaer]

The python server should allow returning trees

[fstwn]

here is an attempt to solve this: https://github.com/fstwn/compute.rhino3d/blob/f4a9c8f49bfffe0bdbf9ec5c72f6083b49b0d1d0/src/ghhops-server-py/ghhops_server/params.py#L194

let me know if there is a way to contribute more directly (i'll also tag @eirannejad since he seems to be quite active on hops development). I would love to constribute in making hops more stable and providing some enhancements.