Postgrest benchmark tests

Verify postgrest version of hivemind.

• check efficiency when we remove MATERIALIZED and double sorting and limiting in functions used by hivemind_endpoints.bridge_api_get_ranked_posts, hivemind_endpoints.bridge_api_get_account_posts and other places.
• Check efficiency of hivemind_endpoints.bridge_api_get_discussion ( !754 (merged) ) and try to optimize that function.