Add ability to scrub from last scrubbed txg

Some users might want to scrub only new data because they would like
to know if the new write wasn't corrupted.  This PR adds possibility
scrub only newly written data.

This introduces new `last_scrubbed_txg` property, indicating the
transaction group (TXG) up to which the most recent scrub operation
has checked and repaired the dataset, so users can run scrub only
from the last saved point. We use a scn_max_txg and scn_min_txg
which are already built into scrub, to accomplish that.

Reviewed-by: Allan Jude <allan@klarasystems.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Mariusz Zaborski <mariusz.zaborski@klarasystems.com>
Sponsored-By: Wasabi Technology, Inc.
Sponsored-By: Klara Inc.
Closes #16301

man/man7/zpoolprops.7

@@ -28,7 +28,7 @@
 .\" Copyright (c) 2021, Colm Buckley <colm@tuatha.org>
 .\" Copyright (c) 2023, Klara Inc.
 .\"
-.Dd July 29, 2024
+.Dd November 18, 2024
 .Dt ZPOOLPROPS 7
 .Os
 .
@@ -135,6 +135,19 @@ A unique identifier for the pool.
 The current health of the pool.
 Health can be one of
 .Sy ONLINE , DEGRADED , FAULTED , OFFLINE, REMOVED , UNAVAIL .
+.It Sy last_scrubbed_txg
+Indicates the transaction group (TXG) up to which the most recent scrub
+operation has checked and repaired the dataset.
+This provides insight into the data integrity status of their pool at
+a specific point in time.
+.Xr zpool-scrub 8
+can utilize this property to scan only data that has changed since the last
+scrub completed, when given the
+.Fl C
+flag.
+This property is not updated when performing an error scrub with the
+.Fl e
+flag.
 .It Sy leaked
 Space not released while
 .Sy freeing