Feature/ Parent-controlled avatar resolver

[jefflau]

A resolver that only allows the parent to set the avatar record.

Should be coupled with a subdomain registrar that forces the resolver to be this resolver on registration and burns CANNOT_SET_RESOLVER at the same time ensuring the resolver.

The resolver inherits from the public resolver and allows all other records to be set as normal. This could also be used with any other record in a similar way.

Built in response to: https://discuss.ens.domains/t/how-to-set-avatar-for-subdomains-upon-registration/16881

Usecases:

• Could be used to create a PFP NFT collection on top of subnames
• Immutable records set by the parent e.g. immutable contenthash/other text records/abi