pgsql: Fix documentation about DROP DATABASE FORCE process termination

Fix documentation about DROP DATABASE FORCE process termination rights.

Specifically, it terminates a background worker even if the caller
couldn't terminate the background worker with pg_terminate_backend().
Commit 3a9b18b3095366cd0c4305441d426d04572d88c1 neglected to update
this.  Back-patch to v13, which introduced DROP DATABASE FORCE.

Reviewed by Amit Kapila.  Reported by Kirill Reshke.

Discussion: https://postgr.es/m/20240429212756.60.nmisch@google.com

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/382284519e141d41f7dc021d6a5fccd5888af8a1

Modified Files
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doc/src/sgml/ref/drop_database.sgml | 12 +++++++-----
src/backend/storage/ipc/procarray.c | 25 ++++++++++++++-----------
2 files changed, 21 insertions(+), 16 deletions(-)