Extend json content handling for referenceAsset

[Walodja1987]

Currently, only URLs that end with .json are handled as json. However, there are also URLs, that do not end with .json but still have json content. Here an example: https://nftstorage.link/ipfs/bafkreic5xs3jg3m4poqqikwyslatiyknkevtwyqqzlouokwlslgkiu5nga

Extend the current check by checking whether the content is of json format by parsing the the response data via JSON.parse.

Dummy code:

async function isJson(url: string): Promise<boolean> {
try {
const response = ...

// Try to parse the content as JSON
try {
JSON.parse(response.data);
return true;
} catch (error) {
return false;
}
}
}