feat: update the api.mustache template and go generator to support JSON media type for the request body

The Go Generator has been updated to add a vendor extension to set `x-is-json` to true when the consume media type is `application/json` and `x-is-form` when the consumes media type is `application/x-www-form-urlencoded`

The `x-is-json` vendor extension is used to generate the code to handle calling the new PostJson function or the corresponding HTTP method function on the request handler. This is designed to only work with Post requests at the moment but could be extended in the future if needed.

This PR aids in resolving twilio#49 however once this PR is merged twilio/twilio-oai#36 will need to be finished to fully resolve the issue

This change relies on twilio/twilio-go#83 and the tests cannot be updated until this PR is merged and released

This change also fixes an issue with JSON struct tags for the Params structs being `html-escaped`. I have disabled the escaping by using `{{{}}}` as this was highlighted during linting the Go SDK repo

Author: RJPearson94

src/main/java/com/twilio/oai/TwilioGoGenerator.java

@@ -1,15 +1,15 @@
 package com.twilio.oai;
 
 import io.swagger.v3.oas.models.OpenAPI;
+import org.openapitools.codegen.CodegenParameter;
+import org.openapitools.codegen.CodegenOperation;
+import org.openapitools.codegen.SupportingFile;
+
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 
-import org.openapitools.codegen.CodegenOperation;
-import org.openapitools.codegen.CodegenParameter;
-import org.openapitools.codegen.SupportingFile;
-
 public class TwilioGoGenerator extends AbstractTwilioGoGenerator {
 
     @Override
@@ -20,10 +20,23 @@ public void processOpts() {
         supportingFiles.add(new SupportingFile("README.mustache", "README.md"));
     }
 
+    @Override
+    public String toApiFilename(String name) {
+        // Drop the "api_" prefix.
+        return super.toApiFilename(name).replaceAll("^api_", "");
+    }
+
+    @Override
+    public void postProcessParameter(final CodegenParameter parameter) {
+        super.postProcessParameter(parameter);
+
+        // Make sure required non-path params get into the options block.
+        parameter.required = parameter.isPathParam;
+    }
+
     @SuppressWarnings("unchecked")
     @Override
-    public Map<String, Object> postProcessOperationsWithModels(final Map<String, Object> objs,
-            final List<Object> allModels) {
+    public Map<String, Object> postProcessOperationsWithModels(final Map<String, Object> objs, final List<Object> allModels) {
         final Map<String, Object> results = super.postProcessOperationsWithModels(objs, allModels);
 
         final Map<String, Object> ops = (Map<String, Object>) results.get("operations");
@@ -44,19 +57,6 @@ public Map<String, Object> postProcessOperationsWithModels(final Map<String, Obj
         return results;
     }
 
-    @Override
-    public String toApiFilename(String name) {
-        // Drop the "api_" prefix.
-        return super.toApiFilename(name).replaceAll("^api_", "");
-    }
-
-    @Override
-    public void postProcessParameter(final CodegenParameter parameter) {
-        super.postProcessParameter(parameter);
-
-        // Make sure required non-path params get into the options block.
-        parameter.required = parameter.isPathParam;
-    }
 
     @Override
     public void processOpenAPI(final OpenAPI openAPI) {