Supports using the `evaluate` request in REPL mode to start a container
with the `exec` command. Presently doesn't support any arguments.
This improves the dap server so it is capable of sending reverse
requests and receiving the response. It also adds a hidden command
`dap attach` that attaches to the socket created by `evaluate`.
This requires the client to support `runInTerminal`.
Likely needs some additional work to make sure resources are cleaned up
cleanly especially when the build is unpaused or terminated, but it
should work as a decent base.
Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>