Add a new command to cli to open vs code fom cli,

It can make use of $CODER_AGENT_URL, and we can further add
$CODER_AGENT_NAME, $CODER_WORKSPACE_NAME, $CODER_USERNAME and $CODER_SESSION_TOKEN
Then a new command like coder vscode from a directory should be able to open vscode using the vscode URI.

Additionally, we can allow vscode-insiders too with coder vscode-insiders

vscode://coder.coder-remote/open?owner={$CODER_USERNAME}&workspace=${CODER_WORKSPACE_NAME}&url=${CODER_AGENT_URL}&token=${CODER_SESSION_TOKEN}&agent=${CODER_AGENT_NAME}&folder=$(pwd)

cc: @bpmct, @kylecarbs, @mafredri
Feedback is welcomed.