feat(service): Add Ntfy service

[nikoksr]

Describe the missing service. Please provide useful links.

Add new service for Ntfy. API docs can be found here.

[pushkar803]

I opened PR for this: #469

[CybersShell]

@nikoksr Hi, I would like to start on implementing this. Is there a way that you would recommend starting? I have the previous pull request for this copied to a branch.

In the years since this was first proposed, the library https://github.com/AnthonyHewins/gotfy was created, and I might use it, barring any objections.

How would you implement tests for this service?