pgsql: Doc: mention CREATE+ATTACH PARTITION with CREATE TABLE...PARTITI

Doc: mention CREATE+ATTACH PARTITION with CREATE TABLE...PARTITION OF.

Clarify that ATTACH/DETACH PARTITION can be used to perform partition
maintenance with less locking than straight CREATE TABLE/DROP TABLE.
This was already stated in some places, but not emphasized.

Back-patch to v14 where DETACH PARTITION CONCURRENTLY was added.
(We had lower lock levels for ATTACH PARTITION before that, but
this wording wouldn't apply.)

Justin Pryzby, reviewed by Robert Treat and Jakub Wartak;
a little further wordsmithing by me

Discussion: https://postgr.es/m/20220718143304.GC18011@telsasoft.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f170b572d2b4cc232c5b6d391b4ecf3e368594b7

Modified Files
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doc/src/sgml/ddl.sgml | 13 +++++++------
doc/src/sgml/ref/create_table.sgml | 20 ++++++++++++++++----
2 files changed, 23 insertions(+), 10 deletions(-)