Add query parameter to filter users by verification state to GET /users API

## Description
As a developer,
I need a filter feature on the Users listing endpoint,
so that I can reuse `GET /users` API to filter users who have the email verified.

`GET /users` API needs a way to filter users by email verification state (which is represented by a boolean value). This will allow us deprecating the extra `GET /users/verified` API.

## Acceptance Criteria
### Update [Required]
- [ ] Add a query parameter support to `GET /users`, to filter by its current state.
- [ ] Update Swagger UI documentation for this API.
- [ ] Write at least one test to prove your new feature is working.

## Definition of Done
- [ ] All of the required items are completed.
- [ ] Approval by 1 mentor.

## Estimation
4 hours