[REG-1430] RegistrarCustody contract

PR Checklist

[x] Make sure that the patch version of the contracts is increased if changes have been made to the UNSRegistry, MintingManager, ProxyReader, ENSCustody contracts.
[ ] Make sure that the minor version of the contracts is increased if breaking changes have been made to the UNSRegistry, MintingManager, ProxyReader, ENSCustody contracts. It includes changes of interfaces.
2. Contracts licensing
[x] Make sure that no SPDX-License-Identifier defined in contracts.

[x] Make sure that the header is added to the new contract files.

// @author Unstoppable Domains, Inc.
// @date {Month} {Day}(ordinal), {Year}

[x] Make sure that the coverage of contracts has not decreased and strive 100%
4. Configs versioning
[x] Make sure that the version of uns-config.json is increased if changes have been made to the config.
[x] Make sure that the version of ens-config.json is increased if changes have been made to the config.
[ ] Make sure that the version of resolver-keys.json is increased if changes have been made to the config.
[ ] Make sure that the version of ens-resolver-keys.json is increased if changes have been made to the config.
5. Package versioning
[x] Make sure that the patch version of package is increased if valuable changes have been made to the package. It includes contracts update, configs update, etc.
[ ] Make sure that the major.minor version of package is synced with version of UNSRegistry contract.
[ ] Make sure that the CHANGELOG is updated with short description for the new version.
6. Code review
[ ] resolver-keys.json code review is required from DevTools team
[ ] ens-resolver-keys.json code review is required from DevTools team
[x] For all other changes code review is required from Registry team