Revert: "refactor(apigateway): Enclose getaway response parameters within single quotes" (#23037)

Reverts #22637

This is because single quotes are _not_ desirable if you're using [context variables](https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-gatewayResponse-definition.html), which must be provided without quotes.

Author: CaerusKaru

Diff for: packages/@aws-cdk/aws-apigateway/README.md

@@ -1378,8 +1378,9 @@ api.addGatewayResponse('test-response', {
   type: apigateway.ResponseType.ACCESS_DENIED,
   statusCode: '500',
   responseHeaders: {
-    'Access-Control-Allow-Origin': 'test.com',
-    'test-key': 'test-value',
+    // Note that values must be enclosed within a pair of single quotes
+    'Access-Control-Allow-Origin': "'test.com'",
+    'test-key': "'test-value'",
   },
   templates: {
     'application/json': '{ "message": $context.error.messageString, "statusCode": "488", "type": "$context.error.responseType" }'

Diff for: packages/@aws-cdk/aws-apigateway/lib/gateway-response.ts

@@ -2,7 +2,6 @@ import { IResource, Resource } from '@aws-cdk/core';
 import { Construct } from 'constructs';
 import { CfnGatewayResponse, CfnGatewayResponseProps } from './apigateway.generated';
 import { IRestApi } from './restapi';
-import { normalizeResponseParameterValue } from './util';
 
 /**
  * Represents gateway response resource.
@@ -89,7 +88,7 @@ export class GatewayResponse extends Resource implements IGatewayResponse {
 
     const responseParameters: { [key: string]: string } = {};
     for (const [header, value] of Object.entries(responseHeaders)) {
-      responseParameters[`gatewayresponse.header.${header}`] = normalizeResponseParameterValue(value) ;
+      responseParameters[`gatewayresponse.header.${header}`] = value;
     }
     return responseParameters;
   }

Diff for: packages/@aws-cdk/aws-apigateway/lib/util.ts

@@ -11,22 +11,6 @@ export function validateHttpMethod(method: string, messagePrefix: string = '') {
   }
 }
 
-/**
- * Response header values need to be enclosed in single quotes.
- */
-export function normalizeResponseParameterValue(value: string) {
-  if (!value) {
-    return value;
-  }
-
-  // check if the value is already enclosed in single quotes
-  if (value.startsWith("'") && value.endsWith("'")) {
-    return value;
-  }
-
-  return `'${value}'`;
-}
-
 export function parseMethodOptionsPath(originalPath: string): { resourcePath: string, httpMethod: string } {
   if (!originalPath.startsWith('/')) {
     throw new Error(`Method options path must start with '/': ${originalPath}`);

Diff for: packages/@aws-cdk/aws-apigateway/test/gateway-response.test.ts

@@ -45,7 +45,6 @@ describe('gateway response', () => {
       responseHeaders: {
         'Access-Control-Allow-Origin': 'test.com',
         'test-key': 'test-value',
-        'another-test': "'test-value-enclosed-within-single-quotes'",
       },
     });
 
@@ -55,9 +54,8 @@ describe('gateway response', () => {
       RestApiId: stack.resolve(api.restApiId),
       StatusCode: '500',
       ResponseParameters: {
-        'gatewayresponse.header.Access-Control-Allow-Origin': "'test.com'",
-        'gatewayresponse.header.test-key': "'test-value'",
-        'gatewayresponse.header.another-test': "'test-value-enclosed-within-single-quotes'",
+        'gatewayresponse.header.Access-Control-Allow-Origin': 'test.com',
+        'gatewayresponse.header.test-key': 'test-value',
       },
       ResponseTemplates: Match.absent(),
     });