API Edit Issue endpoint Documentation lacks detail regarding updated_at field

Summary

An issue's updated_at field can only be edited by an Admin User or the project owner

Documentation proposed

• The updated_at field on an Issue can only be modified via the API by a User authenticating as either an Admin user or the Project owner

Additional detail

Code responsible for the conditional exclusion of the field in the update:

https://gitlab.com/gitlab-org/gitlab-ee/blob/master/lib/api/issues.rb#L126