redis-cli: Accept commands in subscribed mode (#11873)

The message "Reading messages... (press Ctrl-C to quit)" is replaced by
"Reading messages... (press Ctrl-C to quit or any key to type command)".

This allows users to subscribe to more channels, to try out UNSUBSCRIBE and to
combine pubsub with other features such as push messages from client tracking.

The "Reading messages" info message is displayed in the bottom of the output in a
distinct style and moves downward as more messages appear. When any key is pressed,
the info message is replaced by the prompt with for entering commands.
After entering a command and the reply is displayed, the "Reading messages" info
messages appears again. This is added to the repl loop in redis-cli and in the
corresponding place for non-interactive mode.

An indication "(subscribed mode)" is included in the prompt when entering commands
in subscribed mode.

Also:
* Fixes a problem that UNSUBSCRIBE hanged when used with RESP3 and push callback,
  without first entering subscribe mode. It hanged because UNSUBSCRIBE gets one or
  more push replies but no in-band reply.
* Exit subscribed mode after RESET.

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