Closes #96.

If a coder_app exists on the workspace, where the URL is of the form:
coder://dev.coder.com/v0/open/ws/<workspace>/agent/<agent>/rdp?username=administrator&password=password the URL will be parsed, validated, and an alert opened.
If Open is clicked on the alert, the password will be written to the clipboard, where it can be pasted when prompted.

We're unable to avoid the entering of the password, as the password field in an .rdp file, even if encrypted properly, is ignored by the macOS Windows RDP app.

The app supports reading credentials from the macOS keychain, and whilst we could create keychain entries, they have to be associated with an RDP config in the app, and there's no way to automate the creation of that config, and then run that config.

Further reading:
https://stackoverflow.com/questions/48713606/how-to-create-rdp-file-on-mac-os-that-allows-auto-login
https://techcommunity.microsoft.com/discussions/azurevirtualdesktopforum/macos-remote-desktop-client-app---automatic-logon-no-credential-prompt/2596451

The above demo was done by adding this app to the template:

resource "coder_app" "connectrdp" {
  agent_id = coder_agent.main.id
  slug = "connectrdp"
  display_name = "Coder Connect RDP"
  url = "coder://dev.coder.com/v0/open/ws/${data.coder_workspace.me.name}/agent/main/rdp?username=Administrator&password=coderRDP!"
  icon = "/icon/terminal.svg"
  external = true
}