Add configuration to enable turning off spell checking of relation and function names

[mkleczek]

Problem

It seems the issue described in #4463 is caused by hint calculation not being able to handle schemas with a really large number of relations ( see discussion in #4472 (comment) )

The schema that caused #4463 contains around 125k tables. But from the description it seems like the table names are machine generated and not really suitable for spell-checking. (eg. http://{postgrest}/64affa3d080f3180c60b7be3fb97c8b1?limit=20&order=__id.asc)

Solution

Introduce db-spellcheck-enabled configuration property with the default value of true which would allow to disable spell checking of table names in hint calculation.

Fixes #4463