Reduce memory usage by avoiding Aeson encode

It was detected that Aeson encoding had high memory usage when
the json payload was large, around x60 the payload size.
With this change we get around x10 payload size memory usage.

The encodeUtf8(when doing a Text -> ByteString with `toS`) function
on a large payload also contributed to the high memory usage.

Main idea to reduce the memory usage was to let the ByteString coming
from the request body go to the database unchanged.

stack.yaml

@@ -6,6 +6,9 @@ extra-deps:
   - hjsonschema-1.5.0.1
   - Ranged-sets-0.3.0
   - protolude-0.2
+  - hasql-1.1
+  - hasql-pool-0.4.3
+  - hasql-transaction-0.5.2
 ghc-options:
   postgrest: -O2 -Werror -Wall -fwarn-identities -fno-warn-redundant-constraints
 nix: