Add zpool_influxdb command

A zpool_influxdb command is introduced to ease the collection
of zpool statistics into the InfluxDB time-series database.
Examples are given on how to integrate with the telegraf
statistics aggregator, a companion to influxdb.

Finally, a grafana dashboard template is included to show
how pool latency distributions can be visualized in a
ZFS + telegraf + influxdb  + grafana environment.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Richard Elling <Richard.Elling@RichardElling.com>
Closes #10786

cmd/zpool_influxdb/Makefile.am

@@ -0,0 +1,11 @@
+include $(top_srcdir)/config/Rules.am
+
+bin_PROGRAMS = zpool_influxdb
+
+zpool_influxdb_SOURCES = \
+	zpool_influxdb.c
+
+zpool_influxdb_LDADD = \
+	$(top_builddir)/lib/libspl/libspl.la \
+	$(top_builddir)/lib/libnvpair/libnvpair.la \
+	$(top_builddir)/lib/libzfs/libzfs.la