Add IPv6 support

[MAngel666]

Component

UI

Description

It would be nice to have ipv6 settings/support in the WebUI.

[Sn0w3y]

While IPv6 support is generally a good idea for future-proofing, in the context of OpenEMS and local energy management networks,
the practical benefit is quite limited:

1. Energy devices use IPv4: Almost all inverters, batteries, wallboxes, and meters communicate via IPv4 (Modbus TCP, SunSpec, REST
   APIs). These protocols and device implementations are IPv4-based.
2. Local network scope: OpenEMS Edge typically runs in private networks (192.168.x.x, 10.x.x.x) where IPv4 address space is more
   than sufficient for typical installations with 10-50 devices.
3. Added configuration complexity: IPv6 would add complexity for end users without providing tangible benefits in most deployments.
4. No address exhaustion locally: Unlike public internet scenarios, local energy management networks don't face IPv4 address
   scarcity.

Potential edge cases where IPv6 might be relevant:

• Large industrial sites with hundreds of devices
• ISPs providing IPv6-only connectivity (with CGNAT for IPv4)

For now, this seems like a low-priority enhancement. The development effort would likely be better spent on features that address
more common use cases.

That said, if there's a specific deployment scenario where IPv6 is required, please share more details - that context would help
reassess the priority.

[MAngel666]

IPv6 is becoming increasingly widespread and will eventually completely replace IPv4. Some people (like me) are already trying to switch to IPv6 in their LANs to avoid dual-stack configurations.
It's not a high priority, that's clear. But offering communication via IPv6 is simply part of the package these days.