feat: Implementing allOf feature for go (#549)

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# Fixes #

A short description of what this PR does.
Implements allOf feature for go language. Go language implements models
for responses. allOf feature implementation requires creation of new
models with the properties mentioned in the allOf schema. This has to be
referred going forward in the method signatures. This PR also fixes the
bug in api.mustache file where last is referred instead of -last
### Checklist
- [x] I acknowledge that all my contributions will be made under the
project's license
- [ ] Run `make test-docker`
- [ ] Verify affected language:
- [ ] Generate [twilio-go](https://github.com/twilio/twilio-go) from our
[OpenAPI specification](https://github.com/twilio/twilio-oai) using the
[build_twilio_go.py](./examples/build_twilio_go.py) using `python
examples/build_twilio_go.py path/to/twilio-oai/spec/yaml
path/to/twilio-go` and inspect the diff
    - [ ] Run `make test` in `twilio-go`
    - [ ] Create a pull request in `twilio-go`
    - [ ] Provide a link below to the pull request
- [ ] I have made a material change to the repo (functionality, testing,
spelling, grammar)
- [ ] I have read the [Contribution
Guidelines](https://github.com/twilio/twilio-oai-generator/blob/main/CONTRIBUTING.md)
and my PR follows them
- [x] I have titled the PR appropriately
- [ ] I have updated my branch with the main branch
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have added the necessary documentation about the functionality
in the appropriate .md file
- [ ] I have added inline documentation to the code I modified

If you have questions, please create a GitHub Issue in this repository.

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

@@ -138,6 +138,22 @@ public OperationsMap postProcessOperationsWithModels(final OperationsMap objs, L
                     co.returnType = field.dataType;
                     co.returnBaseType = field.complexType;
 
+                    co.vendorExtensions.put("x-payload-field-name", field.name);
+                }
+                //For handling the cases where the schema contains allOf
+                else{
+                    ModelMap modelMap = allModels.stream().filter(map1 -> map1.getModel().getClassname().equals(co.returnType)).collect(toSingleton());
+                    CodegenModel model = (CodegenModel) modelMap.get("model");
+                    final Optional<CodegenModel> returnModelOther = Optional.ofNullable(model);
+                    CodegenProperty field = returnModelOther.get().allVars
+                        .stream()
+                        .filter(v -> v.dataType.startsWith("[]"))
+                        .collect(toSingleton());
+
+                    co.returnContainer = co.returnType;
+                    co.returnType = field.dataType;
+                    co.returnBaseType = field.complexType;
+
                     co.vendorExtensions.put("x-payload-field-name", field.name);
                 }
             }

src/main/resources/twilio-go/api.mustache

@@ -36,7 +36,7 @@ func (params *{{{nickname}}}Params) Set{{paramName}}({{paramName}} {{{dataType}}
 {{#notes}}
 // {{{notes}}}
 {{/notes}}
-func (c *ApiService) {{{nickname}}}({{#allParams}}{{#required}}{{paramName}} {{{dataType}}}{{^last}}, {{/last}}{{/required}}{{/allParams}}{{#hasOptionalParams}}params *{{{nickname}}}Params{{/hasOptionalParams}}) ({{#returnType}}*{{{returnType}}}, {{/returnType}}error) {
+func (c *ApiService) {{{nickname}}}({{#allParams}}{{#required}}{{paramName}} {{{dataType}}}{{^-last}}, {{/-last}}{{/required}}{{/allParams}}{{#hasOptionalParams}}params *{{{nickname}}}Params{{/hasOptionalParams}}) ({{#returnType}}*{{{returnType}}}, {{/returnType}}error) {
     path := "{{{path}}}"
     {{>partial_serialization}}