CDAP-412 REST endpoint to expose Service methods

Endpoint: ``/apps/{app-id}/services/{service-id}/endpoints-exposed``

Example output: 
```
[
    {
        "method": "GET", 
        "path": "/v1/product/{id}/catalog"
    }
]
```


Usually I like the formatting with `throws` is at the end and "righter" then the line above. Something like:

```java
public void visit(Object instance, TypeToken<?> inspectType, 
                         TypeToken<?> declareType, Method method) throws Exception {
```