Add dm3 Resolver to repo

[AlexNi245]

Currently, the Singer-based Resolver dm3 is used as part of the dm3 mono repo.
To have every resolver in one place that resolver should be moved to this repo.
We've to also change the package structure and repo name of this repo to reflect that more than just the Optimism Resolver is included

• Rename repo
• Introduce new package structure
• Move Dm3 Resolver as Offchain Resolver
• Maybe move Gnosis Resolver to EVM Resolver?