feat: add NTP monitor type for network time protocol monitoring

[henricook]

Resolves #5028, builds on the great work by @Jas0n99 on their fork

Summary

In this pull request, the following changes are made:

• Adds a new monitor type that queries NTP servers via UDP

• Parses the response per RFC 5905

• Checks stratum, time offset, and root dispersion against configurable thresholds.

• Resolves NTP check #5028

Checklist

• ⚠️ 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).
• [x]🤖 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

Event	Screenshot
Configuration
NTP Thresholds
UP

[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.

[henricook]

Ready for review! My first contribution, please be gentle 🙏🏻

[smarshall-rightside]

I think there are 2 real issues here:

1. ntp is missing from the hostname validation allowlist in isInputValid() (the ["dns", "port", ... "snmp"] list).
   So NTP hostnames skip the same validation other hostname-based monitors get.

2. In queryNTP() socket family is chosen with hostname.includes(":") ? "udp6" : "udp4".
   That works for literal IPv6 addresses, but not for hostnames that only resolve to AAAA. Those get forced to udp4 and can fail lookup/send.

Could we add ntp to the hostname validation list, and make family selection based on actual DNS result (or fallback udp4 -> udp6)?

[henricook]

Thanks for your time and thoughtful comments @smarshall-rightside . I've added a DNS lookup to gauge ipv4 Vs. ipv6 - there's no precedent for this in the code base but that's because I think I'm dealing with UDP here and not many of the existing monitors have had to think about that. I'd love to know what you think.

Other changes are just tidying up my use of dgram.createSocket

[smarshall-rightside]

Nice addition overall @henricook, thanks for taking the feedback on board. I checked the latest changes and I think the DNS lookup + socket selection is the right call here for UDP/NTP, and the socket lifecycle cleanup looks much safer/cleaner too. Nice addition overall. I'd certainly use it.