contractURI() endpoint

[tbergmueller]

Most market-places support Contract-level metadata (https://docs.opensea.io/docs/contract-level-metadata)
This is being standardized under https://eips.ethereum.org/EIPS/eip-7572

There shall be an endpoint
api/v1/collections/ which returns the collection-Metdata and can be used as contractURI() endpoint.

It shall be compliant with ERC-7572, i.e. always return a name.