Weights do not set system notes

Problem

Weights do not set system notes. With the increased importance of weights when we introduce ~"Portfolio Management" we will need a history to see who changed a weight, similar to milestones.

Proposal

Introduce a system note similar to:

Possible iteration:

Show in the system note if there was already a weight set, from which weight it was changed to which:

similar to https://gitlab.com/gitlab-org/gitlab-ee/issues/3406