Add GraphQL mutation to remove an organization user from a org

Proposal

We need a way for organization admins to remove an organization user from an organization. Build a GraphQL mutation to do this.

Implementation details

Arguments

• id - ID of the organization user to remove

Checks

• :remove_user
  • Consider renaming to :remove_organization_user
• User needs to be in an organization, they cannot be removed unless they are in multiple organizations.
• You cannot remove the last organization admin, there always needs to be one