Allow multiple assignees to an issue in the community edition

Description

GitLab community edition has the multiple assignees feature disabled.

Proposal

Enable it.

Quick Synopsis Of Discussion

• GitLab is not currently, as of 2020-04-30, willing to move multiple assignees down to Core.

Links / references

https://disqus.com/home/discussion/gitlab-docs/multiple_assignees_for_issues_gitlab_documentation/?utm_source=reply&utm_medium=email&utm_content=read_more#comment-3886172658