[REQUEST] Change how Contributors are tracked

[jondricek]

Is your feature request related to a problem? Please describe.

Contributors are tracked today using the x_mitre_contributors field (list of strings) on specific object types. It might be nice to have them tracked by a dedicated STIX object, like the Identity

Describe the solution you'd like
If the STIX Identity object were used to track contributors, then the current practice of each ATT&CK STIX object using the x_mitre_contributors field as a list of strings could still be used, but the strings would be the STIX ids of Identity objects of contributors. This would ultimately make it easier to interact with Contributor objects in the Mongo DB.

Describe alternatives you've considered

I have only really considered the approach mentioned above so far, but open to other suggestions.

Additional context

The ATT&CK website has the poor practice of manually adding some contributors after the fact since they are not directly connected to specific objects, while still contributing to ATT&CK. This feature request would help make this scenario be able to be handled in STIX directly instead of a random python script generating a webpage.

https://github.com/mitre-attack/attack-website/blob/master/modules/util/stixhelpers.py#L428-L429