main: display a message when local console is exited

Consider the following example:
```
tarantool -e "box.cfg{} require('console').start()"
```
When a local console is exited by pressing Ctrl+D, Tarantool seemingly
freezes - console stops to work, typed characters are not echoed. But
the event loop is not stopped because there are background fibers running.
This patch adds a message that Ctrl+C should be pressed in such a case.

Closes #7017

NO_DOC=minor