Slow `count(*)` for large table

Try to totally remove it or use an alternative method (information_schema)

• https://dba.stackexchange.com/questions/151769/mysql-difference-between-using-count-and-information-schema-tables-for-coun

• information_schema gives a approximation result.
• If there is a 'where' predicate, it cannot be applied on select from information_schema. The result will be larger than expected.

8c39073:

Counting with select count(*) by default. Set env var DTLE_COUNT_INFO_SCHEMA=anything_not_empty when start dtle server to use infomation_schema.

3c66ecb: CountTableRows with information_schema.

Consequence: there might be a huge difference between estimated and actual number of rows, when where is used.