pgsql: Increase upper limit for vacuum_cleanup_index_scale_factor

Increase upper limit for vacuum_cleanup_index_scale_factor

Upper limits for vacuum_cleanup_index_scale_factor GUC and reloption
were initially set to 100.0 in 857f9c36.  However, after further
discussion, it appears that some users like to disable B-tree cleanup
index scan completely (assuming there are no deleted pages).

vacuum_cleanup_index_scale_factor is used barely to protect against
stalled index statistics.  And after detailed consideration it appears
that risk of stalled index statistics is low.  And it would be nice to
allow advanced users setting higher values of
vacuum_cleanup_index_scale_factor.  So, set upper limit for these
GUC and reloption to DBL_MAX.

Author: Alexander Korotkov
Reviewed-by: Masahiko Sawada
Discussion: https://postgr.es/m/CAC8Q8tJCb%3DgxhzcV7T6ctx7PY-Ux1oA-AsTJc6cAVNsQiYcCzA%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6ca33a885bf892a7fa34020a2620c83ccec3cdd7

Modified Files
--------------
doc/src/sgml/config.sgml                  | 2 +-
src/backend/access/common/reloptions.c    | 2 +-
src/backend/access/nbtree/nbtree.c        | 8 +++++---
src/backend/utils/misc/guc.c              | 2 +-
src/test/regress/expected/btree_index.out | 2 +-
5 files changed, 9 insertions(+), 7 deletions(-)