use md5 hash as a id for MetadataEntity

[vikiival]

Describe the feature

Currently we are using metadata string as a id for metadata entity and it is not very kosher.
therefore -> entity.metadata === meta.id

Expected outcome

I expect to use md5 to hash metadata id so -> md5(entity.metadata) === meta.id
additionally we can implement #223 like token.id === md5(meta.image) + ':' md5(meta.animation_url)

Reference

Additional context

CC @daiagi