Support individual NFT metadata logs / dynamic NFTs

[telezhnaya]

Inspired by #423 (comment)

The highlights from the thread:
[...] the proposal of individual NFT metadata updates opened a whole can of worms ("dynamic" NFTs etc) so it was decided to separate these into their own PRs [...].

See original discussion here: https://gov.near.org/t/extending-nep-171-events-standard-to-include-nft-update-events/30285/6

[...]

We may want to track even updates from dynamic NFTs, that will give us the ability to show the evolution of the NFT, so we anyway may need the logs for that.
Or at least we may want to know if the NFT is dynamic or not, it requires one more extension, adding the flag to the metadata. And maybe some other information such as the frequency of the updates, etc. We definitely need to research it deeper. We can post any further ideas here

[codingshot]

This was one of the concerns I initially made and I think this would save capabilities for indexers. If we are adding flags might as well do this for Rich Media so indexers know which type of file type they are indexing without going into the metadata. Lachlan has also expressed concerns about this but was going to submit as different NEP extension. This has also been an indexing issue for our marketplace as well.