Implement complete labels API (create/delete/update)

Created by: Razer6

What does this MR do?

As labels got their color feature, the API also needs some ❤.

This PR adds the following features:

• Create a new label via API
• Delete existing labels via API
• Update existing label via API

Are there points in the code the reviewer needs to double check?

Creating a new label is refactored out to a service.

Why was this MR needed?

Currently, the API can only get labels

@jvanbaarsen Could you review 😇