feat: add ntfy notifications

[frostplexx]

This PR adds support for ntfy.sh notifications.

[Lukap22]

I need this!

[vinicius507]

What are the plans for this integration?

[gitguardian]

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[peaklabs-dev]

@frostplexx Sorry for the late review. I have completed the refactored notifications for the next release and if you still have time and are able to work on this PR, it would be necessary to adjust your PR according to the new notification handling. You can check my PR to see the migrations and models added: #4525 and you can check out the next branch for now to see the new way of implementing notifications.

It would be great if you could adjust your PR accordingly. If you are unable to do so, please let me know so I can close this PR.

[compgeniuses]

the new refactored notifications is superb