pgsql: Introduce num_os_semaphores GUC.

Introduce num_os_semaphores GUC.

The documentation for System V IPC parameters provides complicated
formulas to determine the appropriate values for SEMMNI and SEMMNS.
Furthermore, these formulas have often been wrong because folks
forget to update them (e.g., when adding a new auxiliary process).

This commit introduces a new runtime-computed GUC named
num_os_semaphores that reports the number of semaphores needed for
the configured number of allowed connections, worker processes,
etc. This new GUC allows us to simplify the formulas in the
documentation, and it should help prevent future inaccuracies.
Like the other runtime-computed GUCs, users can view it with
"postgres -C" before starting the server, which is useful for
preconfiguring the necessary operating system resources.

Reviewed-by: Tom Lane, Sami Imseih, Andres Freund, Robert Haas
Discussion: https://postgr.es/m/20240517164452.GA1914161%40nathanxps13

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/0dcaea56903489e8abedf231f286272495c3beb4

Modified Files
--------------
doc/src/sgml/config.sgml | 18 ++++++++++++++++++
doc/src/sgml/runtime.sgml | 31 +++++++++++++++++++------------
src/backend/storage/ipc/ipci.c | 6 +++++-
src/backend/utils/misc/guc_tables.c | 12 ++++++++++++
4 files changed, 54 insertions(+), 13 deletions(-)