Bulk editing issues I'm not already subscribed to or participating in should not subscribe me

Implementation

We want to do this by adding some metadata to system notes that decides whether the note author was participating.

• https://gitlab.com/gitlab-org/gitlab-ce/issues/24784 is a proposal to add a table for system note metadata, and blocks this.
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7535 does this with the main notes table, and can probably be adapted (with credit to the author, as it's a ~"Community Contribution") to do the same on the metadata table.

Original description

When a release passes, and I bulk move all issues that are still open from that old milestone to a new one, a system note is created on every one of them saying I changed the milestone, which also results in me becoming a participant of those issues, and me getting email notifications for every thing that happens on those issues, going forward. I think a bulk action does not mean I'm interested in that issue to the extent that I want to know everything that happens to it after that action. A bulk edit should not subscribe me to issues that I wasn't already subscribed to or participating to.

Of course I do still want to be subscribed and receive notifications when I change the milestone while looking at the issue page itself, since I am then directly interacting with that specific issue, which makes it more likely that I am interested in it in some capacity. If not, the "Unsubscribe" link is available on that same page.