Go Lambda broken for non-ApiGateway handlers with custom request/response types (e.g AppSync)

## Bug Report

**Current Behavior**

When mounting the handler code directly (e.g. not passing `--useDocker`) the app will fail to run if the handler function signature is not one of the expected `ApiGateway` request structs.

It looks like support was added last year by @icarus-sullivan via #1320 using https://github.com/icarus-sullivan/mock-lambda for wrapping the `lambda.Start` function. The version included in serverless-offline seems to have a strict requirement for what the handler function signature should look like:

```go
if authorizer != "true" {
response = api(h.(func(ctx context.Context, request events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error)))
}

if authorizer == "true" && tokenAuthorizer == "true" {
response = token(h.(func(request events.APIGatewayCustomAuthorizerRequest) (events.APIGatewayCustomAuthorizerResponse, error)))
}

if authorizer == "true" && requestAuthorizer == "true" {
response = request(h.(func(request events.APIGatewayCustomAuthorizerRequestTypeRequest) (events.APIGatewayCustomAuthorizerResponse, error)))
}
```

However, a lambda function may have a custom request or response type - this is particularly true if the Lambda function is being used with Appsync. As a result the app will fail to run due to an interface conversion error:

```
panic: interface conversion: interface {} is func(context.Context, map[string]interface {}) (app.User, error), not func(context.Context, events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error)
```

**Sample Code**

- file: main.go

Example from aws: https://docs.aws.amazon.com/lambda/latest/dg/golang-handler.html

```go
package main

import (
"fmt"
"context"
"github.com/aws/aws-lambda-go/lambda"
)

type MyEvent struct {
Name string `json:"name"`
}

func HandleRequest(ctx context.Context, name MyEvent) (string, error) {
return fmt.Sprintf("Hello %s!", name.Name ), nil
}

func main() {
lambda.Start(HandleRequest)
}
```

**Expected behavior/code**

serverless-offline should support handlers with custom request/response types

**Environment**

- `serverless` version: v3.28.1
- `serverless-offline` version: 12.0.4

**Additional context/Screenshots**

- This may also be related to #1478