Validate bool query params as enum, not presence

Addresses the following review comments:
- #162 (comment)
- #162 (comment)
- #162 (comment)

Author: feuGeneA

src/handlers/swap_handlers.ts

@@ -180,12 +180,10 @@ const parseGetSwapQuoteRequestParams = (req: express.Request): GetSwapQuoteReque
     const rfqt =
         req.query.intentOnFilling === undefined
             ? undefined
-            : {
-                  intentOnFilling: ['true', ''].includes(req.query.intentOnFilling) ? true : false,
-              };
+            : { intentOnFilling: req.query.intentOnFilling === 'true' ? true : false };
     // tslint:disable-next-line:boolean-naming
     const skipValidation =
-        req.query.skipValidation === undefined ? false : ['true', ''].includes(req.query.skipValidation) ? true : false;
+        req.query.skipValidation === undefined ? false : req.query.skipValidation === 'true' ? true : false;
     return {
         takerAddress,
         sellToken,

src/schemas/swap_quote_request_schema.json

@@ -27,11 +27,11 @@
         },
         "intentOnFilling": {
             "type": "string",
-            "allowEmptyValue": true
+            "enum": ["true", "false"]
         },
         "skipValidation": {
             "type": "string",
-            "allowEmptyValue": true
+            "enum": ["true", "false"]
         }
     },
     "required": ["sellToken", "buyToken"],