Local network restriction does not support IPv6 global unicast addresses

### The problem

The "can only log in from the local network" restriction on users doesn't work when the network uses IPv6 global unicast addresses (2000::/3) because only unique local addresses (fd00::/8) are considered to be local.

The local IPv6 network needs to be auto-detected and/or the IP addresses that are considered to be in "the local network" needs to be configurable.

### What version of Home Assistant Core has the issue?

2023.7.3

### What was the last working version of Home Assistant Core?

_No response_

### What type of installation are you running?

Home Assistant Core

### Integration causing the issue

_No response_

### Link to integration documentation on our website

_No response_

### Diagnostics information

_No response_

### Example YAML snippet

_No response_

### Anything in the logs that might be useful for us?

_No response_

### Additional information

_No response_

The issue names no file or test. Start by locating Home Assistant Core's local-network login restriction and the IPv6 address classification it uses; reproduce the failure with a 2000::/3 address. Done means the restriction correctly handles the intended local IPv6 network behavior, with tests covering the chosen detection or configuration approach.

Written by the indexing model from the issue text.