pgsql: Fix documentation for pg_stat_recovery_prefetch.

Fix documentation for pg_stat_recovery_prefetch.

The table was in the wrong section and using an older type of link, as
reported by Sirisha, and also using an older table layout, as I noticed
while trying to figure out how and when it might have got out of sync.

Defect in commit 5dc0418f.

Author: sirisha chamarthi <sirichamarthi22(at)gmail(dot)com>
Author: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAKrAKeVk-LRHMdyT6x_p33eF6dCorM2jed5h_eHdRdv0reSYTA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4533de358dd5f2a8930e3a73bcb49103b37357be

Modified Files
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doc/src/sgml/monitoring.sgml | 193 ++++++++++++++++++++++++++++---------------
1 file changed, 126 insertions(+), 67 deletions(-)