IPv6 examples using invalid internal addresses

### Template files

- ipv6-in-vnet/azuredeploy.json
- ipv6-in-vnet-StdLB/azuredeploy.json
- ipv6-in-vnet-vmss/azuredeploy.json

### Documentation Examples:

https://docs.microsoft.com/bs-latn-ba/azure/virtual-network/ipv6-configure-template-json
https://docs.microsoft.com/en-us/azure/virtual-network/virtual-network-ipv4-ipv6-dual-stack-powershell
https://docs.microsoft.com/bs-latn-ba/azure/virtual-network/ipv6-add-to-existing-vnet-cli

### Issue Details
These use the IPv6 address space:

`ace:cab:deca::/48`

ipv6 addresses for internal networks which appear to be reserved addresses.

https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml

Internal networks should use Unique Local address space:

`fc00::/7`

All templates and training materials should be updated to avoid using reserved address space. Azure internal networks are not routable so Unique Local address space seems appropriate.

`fcce:cab:deca::/48` would work. Not sure where the current invalid ipv6 space came from. It would be better to to generate a unique Global ID which might then allow different groups to route traffic eventually. Perhaps suggest internal space based on some part of the UUID of the VNET?

https://tools.ietf.org/html/rfc4193

If the examples move to Unique Local Addresses, the deployed OS will prefer IPv4 over IPv6 for getaddressinfo() as in RFC-6724 (was RFC-3484)

https://tools.ietf.org/html/rfc6724

On Ubuntu, this means editing /etc/gai.conf where I uncommented this lines:

```
label ::1/128 0
label ::/0 1
label 2002::/16 2
label ::/96 3
label ::ffff:0:0/96 4
label fec0::/10 5

```

Start with ipv6-in-vnet/azuredeploy.json, ipv6-in-vnet-StdLB/azuredeploy.json, and ipv6-in-vnet-vmss/azuredeploy.json, then review the linked IPv6 documentation examples. Compare the current ace:cab:deca::/48 values with the IANA registry and RFC 4193. Done means the templates and training materials no longer use invalid reserved internal space and consistently use an appropriate Unique Local address range.

Written by the indexing model from the issue text.