Fix for count being very slow on large Parse Classes' collections (Postgres) (#5330)

* Changed count to be approximate. Should help with postgres slowness

* refactored last commit to only fall back to estimate if no complex query

* handlign variables correctly

* Trying again because it was casting to lowercase table names which doesnt work for us/

* syntax error

* Adding quotations to pg query

* hopefully final pg fix

* Postgres will now use an approximate count unless there is a more complex query specified

* handling edge case

* Fix for count being very slow on large Parse Classes' collections in Postgres. Replicating fix for Mongo in issue 5264

* Fixed silly spelling error resulting from copying over notes

* Lint fixes

* limiting results to 1 on approximation

* suppress test that we can no longer run for postgres

* removed tests from Postgres that no longer apply

* made changes requested by dplewis

* fixed count errors

* updated package.json

* removed test exclude for pg

* removed object types from method

* test disabled for postgres

* returned type

* add estimate count test

* fix mongo test

src/Adapters/Storage/StorageAdapter.js

@@ -86,7 +86,8 @@ export interface StorageAdapter {
     className: string,
     schema: SchemaType,
     query: QueryType,
-    readPreference: ?string
+    readPreference?: string,
+    estimate?: boolean
   ): Promise<number>;
   distinct(
     className: string,