gp open/preview should await till UI is available

[akosyakov]

Bug description

Otherwise they can break in tasks currently: https://community.gitpod.io/t/using-code-or-gp-open-in-start-tasks-fail-hard/3376

Steps to reproduce

See above.

Expected behavior

No response

Example repository

No response

Anything else?

No response

[svenefftinge]

Do we want to have an explicit command that awaits a connection of a code editor and then also internally use it from the two mentioned commands?

[JanKoehnlein]

Do we want to block on opening editors until the IDE is ready? This could be problematic when misused in non-interactive scenarios (like init in prebuilds). I'm not sure if we'd rather want an async-open command that retries than force blocking. Can we detect whether we run in a prebuild?

The code CLI connects to the Gitpod code server via REST. The CLI would have to retry until the server is up and an IDE client has connected. But we could also add that retry logic for all CLI commands that delegate to the server. Should we?

[akosyakov]

Maybe we can detect that we are in prebuild context and fail then.

[apolopena]

Just a note that the error message has changed (as a result of resolving issue #3195) from:
error while issuing request: Post "http://localhost:23000/gitpod/cli": context deadline exceeded (Client.Timeout exceeded while awaiting headers)
to:
Bad status code: 404: Not found.

This is a pesky bug because it can make the user experience intermittently poor when the preview browser cannot be opened.