MEDIUM: cli: make the prompt mode configurable between n/i/p

MEDIUM: cli: make the prompt mode configurable between n/i/p

Now the prompt mode can more finely be configured between non-interactive
(default), interactive without prompt, and interactive with prompt. This
will ease the usage from automated tools which are not necessarily
interested in having to consume '> ' after each command nor displaying
"+" on payload lines. This can also be convenient when coming from the
master CLI to keep the same output format.