Support IP address for anchor's test servers

[lijamie98]

Slack Discussion: https://stellarfoundation.slack.com/archives/C01JU2888MP/p1728939684760049

What problem does your feature solve?

Currently, the home_domain of the anchor's server must be "domains". IP addresses are not allowed.

What would you like to see?

We want to test anchor servers without domain. ie: IP addresses.

What alternatives are there?

Ask the anchor to host domains. But I can imagine the convenience of using the IP addresses.

[quietbits]

We currently don't have an IP address to test this with. Putting on hold for now.