expose data about transfers in progress

BIND user with lots of zones wants data to monitor and troubleshoot zone transfers to be available.

Expose stats like:

Zone	State	Source IP	Source port	Protocol	Duration [s]	Bytes received
1example.com	Receiving	192.0.2.1	53	TCP	69	6845
2example.com	Applying delta	192.0.2.1	853	TLS	5	900
3example.com	IXFR-from-differences	192.0.2.1	53	TCP	5	7896

See what else would be useful - #3883 (comment 354966).

Edited Mar 03, 2023 by Petr Špaček

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