Add jupyter-sshd-proxy

Over at LEAP we have been testing https://github.com/yuvipanda/jupyter-sshd-proxy (thanks @yuvipanda )and it works really nicely to connect to cloud hubs e.g. using vscode. I think this is a pretty broadly requested functionality and thus would be a good addition here.

Not sure about the pip dependency in this file. Should live somewhere else?

cc @dhruvbalwada

pangeo-notebook/environment.yml

@@ -81,6 +81,9 @@ dependencies:
  - panel
  - parcels
  - param
+ - pip
+ - pip:
+     jupyter-sshd-proxy
  - planetary-computer
  - pop-tools
  - pyarrow