doc: Consistently spell case-insensitive
While almost all occurrences of "case-insensitive{ly}" were spelled with
a dash, a few were using "case insensitive{ly}" with a space instead. Fix
by changing these to use a dash to be consistent.
Discussion: https://postgr.es/m/
7657EDEE-5EE2-4AAB-BA95-
47B4F71653E1@yesql.se