[cli] Implement a `gp` command to get preview URLs

[jankeromnes]

Some projects' development servers only accept requests with a pre-specified host (e.g. localhost, or example.com) and any request using a different host will get dropped (for example Gitpod preview URLs). Note: This is orthogonal to binding ports on localhost or 0.0.0.0.

@32leaves suggested we could have a gp command that returns preview URLs.

I suggest the following new feature:

$ gp preview-url 4242
https://4242-abcdef01-2345-6789-81e5-e7f1005fb9c8.ws-eu.gitpod.io/

Should we also have a way to list currently running ports? Or maybe implement auto-complete for this? Comments/suggestions very welcome.

[jankeromnes]

Note: There are already similar commands like gp url and gp preview:

$ gp url
https://abcdef01-2345-6789-81e5-e7f1005fb9c8.ws-eu.gitpod.io/

$ gp preview http://nyan.cat
# opens given URL in Preview

To stay consistent, maybe my suggested gp preview-url 4242 should be a parameter for gp url instead? E.g. gp url 4242 or gp url --port=4242.

[jankeromnes]

Another idea if we add preview URLs to gp url could be to have a gp url -a or gp url --all:

$ gp url --all
Workspace   https://abcdef01-2345-6789-81e5-e7f1005fb9c8.ws-eu.gitpod.io/
Port 4242   https://4242-abcdef01-2345-6789-81e5-e7f1005fb9c8.ws-eu.gitpod.io/
Port 8080   https://8080-abcdef01-2345-6789-81e5-e7f1005fb9c8.ws-eu.gitpod.io/

[jankeromnes]

Oh, wow, it actually exists already:

$ gp help url
Prints the URL of this workspace. This command can print the URL of
the current workspace itself, or of a service running in this workspace on a
particular port. For example:
    gp url 8080
will print the URL of a service/server exposed on port 8080.

Usage:
  gp url [port] [flags]

Flags:
  -h, --help   help for url

$ gp url 4242
https://4242-abcdef01-2345-6789-81e5-e7f1005fb9c8.ws-eu.gitpod.io/

That was easy!