Add missing types to the sysctl(9) manual page

Update the diff to include other missing sysctl types found in sysctl.h.

Some of these sysctls are already documented in other pages (e.g counter(9)
and ZONE(9)), but they should at least be mentioned here for completeness.

This patch now documents all of the following:

• SYSCTL_BOOL/SYSCTL_ADD_BOOL
• SYSCTL_COUNTER_U64/SYSCTL_ADD_COUNTER_U64
• SYSCTL_COUNTER_U64_ARRAY/SYSCTL_ADD_COUNTER_U64_ARRAY
• SYSCTL_SBINTIME_MSEC/SYSCTL_ADD_SBINTIME_MSEC
• SYSCTL_SBINTIME_USEC/SYSCTL_ADD_SBINTIME_USEC
• SYSCTL_UMA_CUR/SYSCTL_ADD_UMA_CUR
• SYSCTL_UMA_MAX/SYSCTL_ADD_UMA_MAX

Submitted by: mhorne063_gmail.com
Reviewed by: bcr, hselasky
Approved by: bcr (doc), hselasky (src)
Approved by: krion (mentor, implicit), mat (mentor, implicit)
Differential Revision: https://reviews.freebsd.org/D19272