feat: Add Pinglet notification provider

[TheGlenn88]

Summary

In this pull request, the following changes are made:

Add Pinglet as a notification provider

Please follow this checklist to avoid unnecessary back and forth (click to expand)

• ⚠️ If there are Breaking change (a fix or feature that alters existing functionality in a way that could cause issues) I have called them out
• 🧠 I have disclosed any use of LLMs/AI in this contribution and reviewed all generated content.
  I understand that I am responsible for and able to explain every line of code I submit.
• 🔍 Any UI changes adhere to visual style of this project.
• 🛠️ I have self-reviewed and self-tested my code to ensure it works as expected.
• 📝 I have commented my code, especially in hard-to-understand areas (e.g., using JSDoc for methods).
• 🤖 I added or updated automated tests where appropriate.
• 📄 Documentation updates are included (if applicable).
• 🧰 Dependency updates are listed and explained.
• ⚠️ CI passes and is green.

Screenshots for Visual Changes

[github-actions]

Thanks for the PR! If anyone would like to help with testing, run: npx kuma-pr TheGlenn88:pinglet-notification-provider (requires Node.js and Docker)

[github-actions]

Hello and thanks for lending a paw to Uptime Kuma! 🐻👋
As this is your first contribution, please be sure to check out our Pull Request guidelines.
In particular: - Mark your PR as Draft while you’re still making changes - Mark it as Ready for review once it’s fully ready
If you have any design or process questions, feel free to ask them right here in this pull request - unclear documentation is a bug too.

[github-actions]

@TheGlenn88 congrats on your first contribution to Uptime Kuma! 🐻
We hope you enjoy contributing to our project and look forward to seeing more of your work in the future! If you want to see your contribution in action, please see our nightly builds here.