Add fallback to 'image_url' if 'animation_url' is invalid for NFT instance

[yvaskov]

Description

We are currently prioritizing animation_url before image_url without a fallback option.

In this example animation_url from the instance metadata has invalid content, hence we show no image, even with image_url present:
https://explorer.immutable.com/token/0x848cDb63B09490189E8D9779b5aE7782dA9A40EE/instance/45186
https://metadata.guildofguardians.com/api/v1/nfts/0x848cdb63b09490189e8d9779b5ae7782da9a40ee/45186

Need to implement a fallback option to image_url when animation_url content is invalid.

[yvaskov]

Assigned critical severity as it impacts Immutable mainnet collections

[tom2drum]

also we can add support for .m3u8 files
example

UPDATE: will do in a separate task #1671