feat(notifications): add Ntfy as notification provider

[ShadowArcanist]

Changes

• Added Ntfy as notification provider, with options to select auth types and message priorities

Issues

• Fixes Instance notifications integration with ntfy #5001 and ntfy Notifications Provider #8155

Category

• New feature

Preview

AI Assistance

• AI was used (please describe below)

If AI was used:

• Tools used: Jean + Claude (Opus 4.6)
• How extensively: every change on this PR (except the PR description)

Testing

• Tested all types of auth with self hosted ntfy instance and message priorities with both self hosted ntfy + cloud hosted (public instance)
• For notification types I only tested deployment success, deployment failure, Instance backup success, Docker clean up success

Contributor Agreement

Important

• I have read and understood the contributor guidelines. If I have failed to follow any guideline, I understand that this PR may be closed without review.
• I have searched existing issues and pull requests (including closed ones) to ensure this isn't a duplicate.
• I have tested all the changes thoroughly with a local development instance of Coolify and I am confident that they will work as expected when a maintainer tests them.

[github-actions]

Hi @ShadowArcanist! 👋

It appears to us that you are adding a new feature to Coolify.
We kindly ask you to also update the Coolify Documentation to include information about this new feature.
This will help ensure that our documentation remains accurate and up-to-date for all users.

Coolify Docs Repository: https://github.com/coollabsio/coolify-docs
How to Contribute to the Docs: https://coolify.io/docs/get-started/contribute/documentation