[Core] Resolve metadata for domains & addresses (i.e. `avatar` field)

[wottpal]

Resolve specific metadata for domains & addresses. This could be:

• The avatar field. Additionally, as the avatar field can be not only an URL but also ENSIP-12-compatible PSP34 NFT's in the future, there might need to be some URL resolving within the library to ease integration.
• The display field stores a certain way of domain name capitalization (e.g. to display AlephZero.azero). This is also blocked by the frontend to support the entry of this value & add documentation about it.