pgsql: Doc: improve descriptions of max_[pred_]locks_per_transaction GU

Doc: improve descriptions of max_[pred_]locks_per_transaction GUCs.

The old wording described these as being multiplied by max_connections
plus max_prepared_transactions, which hasn't been exactly right for
some time thanks to the addition of various auxiliary processes.
Moreover, exactness here is a bit pointless given that the lock tables
can expand into the initially-unallocated "slop" space in shared
memory.  Rather than trying to track exactly what the code is doing,
let's just use the term "server processes".

Likewise adjust these GUCs' description strings in guc_tables.c.

Wang Wei, reviewed by Nathan Bossart and myself

Discussion: https://postgr.es/m/OS3PR01MB6275BDD09C9B875C65FCC5AB9EA39@OS3PR01MB6275.jpnprd01.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ff245a37888ae28da4e6eeacac83f00aa0986340

Modified Files
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doc/src/sgml/config.sgml            | 28 +++++++++++++---------------
src/backend/utils/misc/guc_tables.c | 10 +++++-----
2 files changed, 18 insertions(+), 20 deletions(-)