Add BIND application version as label to bind_up metric

[smbambling]

Host operating system
ubuntu22.04.1 ( container )

BIND version
9.18.28

bind_exporter version
0.7.0

bind_exporter command-line flags
--bind.stats-url http://bind9:8053

It would be very helpful for tracking the installed version of BIND if the application version were a label that could be queried.