Add command to run a `coder speedtest` against a workspace

[spikecurtis]

coder speedtest tests the end-to-end connection speed of the tailnet tunnel to a workspace. Add this as an optional command to allow users to diagnose whether any perceived slowness is attributable to the networking.

It includes a JSON output format like:

Starting a 5s download test...
{
  "overall": {
    "start_time_seconds": 0,
    "end_time_seconds": 5.0410079,
    "throughput_mbits": 911.9123149955785
  },
  "intervals": [
    {
      "start_time_seconds": 0,
      "end_time_seconds": 1.0028376,
      "throughput_mbits": 803.0276966081047
    },
    {
      "start_time_seconds": 1.0028376,
      "end_time_seconds": 2.0064851,
      "throughput_mbits": 819.0959315895271
    },
    {
      "start_time_seconds": 2.0064851,
      "end_time_seconds": 3.0181882,
      "throughput_mbits": 961.8222263033492
    },
    {
      "start_time_seconds": 3.0181882,
      "end_time_seconds": 4.0363963,
      "throughput_mbits": 988.6318523688822
    },
    {
      "start_time_seconds": 4.0363963,
      "end_time_seconds": 5.0410079,
      "throughput_mbits": 985.311879735412
    }
  ]
}

which lends itself to plotting or other nice graphical outputs.

[EhabY]

For the UX, should it be a simple Command like Coder: Speed Test? Also where would we output the JSON (potentially we can just show the full output in a terminal and they can copy paste if need be)?

The discussion here would probably also apply to #749

[EhabY]

@code-asher @jcjiang would appreciate some feedback on the UX of #749, #750, #751

[code-asher]

Yeah I think implementing them as commands is the way to go. We can always then later hook up buttons to those commands if we need to make them more discoverable, from the sidebar or something.

For the speed test, what if it asked whether the user wanted it in their clipboard (assuming extensions have access to the clipboard) or as a new file (after which users can then save it to disk, or if we have access to the file save dialog we could create the file directly for them).

Or we just open it as a new file, at which point a user can either save to disk or select all and copy (although unfortunately that would require that they then close the file and say no to the unsaved changes prompt, which could feel a bit janky).

Or do we maybe want to pop open a web view and render the data as a graph right there in the editor (with buttons to view the raw data as a new file or copy it)?

For ping in #749, I think popping open a terminal and running it in there makes a lot of sense, similar to how a build command would work.

And for the support bundle #751 we could also run this in the terminal, might make the most sense since it has some output the user should probably read and we probably want them to answer yes to the confirmation prompt.