Proxy Docker connection to the terminal to be served over the web terminal websocket connection

Problem to solve

Proxy docker connection to the terminal to be served over the websocket connection.

Further details

In gitlab-runner#3467 (closed) support for the docker executor will be added for the interective web terminal. The runner will need a way to proxy the STDOUT/STDIN/STDERR from the docker container to the WebSocket.

Proposal

The executor will handle the generation of the connection, the gitlab-terminal has to proxy types.HijackedResponse to the websocket, something similar to what the file descriptor/web socket proxy is doing.

Related issues

gitlab-runner#3467 (closed)

gitlab-org/gitlab-ce#25990