Fix documentation for System V semaphores.

Fix documentation for System V semaphores.

The formulas for SEMMNI and SEMMNS do not include the archiver
process, which was converted to an auxiliary process in v14, and
the WAL summarizer process, which was introduced in v17.  This
commit corrects these formulas and adds a missing reference to
max_wal_senders nearby.  Since this section of the documentation
tends to be incorrect quite often, we should likely give up on
documenting the exact formulas in favor of something less fragile,
but that is left as a future exercise.

Reported-by: Sami Imseih
Reviewed-by: Sami Imseih
Discussion: https://postgr.es/m/20240517164452.GA1914161%40nathanxps13
Backpatch-through: 12