Employees can comment on other colleagues' gif post

### Why

**As an Employee**
**I want to be able to comment on other colleagues' gif post**
**So that my comment can be posted and seen by other colleagues**

### Acceptance Criteria

```gherkin
Scenario: 
Given that an employee make a post request on this endpoint (i.e api/v1/gifs/<gifId>/comment)
When the comment is written
Then such comment will be posted
```

