Add domain validation

[ya7010]

Related: #5621

Prohibit the use of the json.schemastore.org domain and recommend the use of www.schemastore.org instead.

To pass CI for this PR, we need to merge #5626 first.

[madskristensen]

this is a great idea, but the issue is that the current $id property URLs must not change and they have to remain using json.. But perhaps we can limit it to new files or to $ref URLs instead?

[ya7010]

Conceptually, I understand that the $id should not be changed, but in practice, json.schemastore.org redirects to www.schemastore.org.

What are some potential drawbacks of changing the $id?