[NIP05 BE] Prevent users from signing up with Nos Team user names

[setch-l]

Users signing up for a NIP05 user name who are outside the nos team, should not be able to use the names on this list.

https://www.notion.so/nossocial/Blocked-internal-NIP05-names-7164550b5b894464be1f445dfe847998

[dcadenas]

I'll add some feedback I got from @martindsq here, let's limit the name size also to something like 30, like instagram does.