Add a coder open rdp command

[bpmct]

Background: Notion. There are some ideas/questions in there around implimentation.

Add a coder open rdp command that can forward an RDP port and auto-fill the details (host, username, and password into an RDP client. Like port forward, the command can hang and when cancelled it can disconnect the session. I'm not sure if we should only enable this for workspaces with specific attributes (Windows) or just fail if there is no RDP port open on the workspace

Related: coder/modules#234

[bpmct]

Related is https://github.com/coder/customers/issues/572. I wonder if we can make coder open more generic / extensible by modules (e.g. forward local ports, open browser, etc)