Issues to apply severity and priority for Plan

Here is a list of issues without severity and priority:

• Unauthorized epic participation for groups you are not a member of ~"Plan", ~"bug", ~"devops:plan", epics
• filename Syntax search filter does not work as in docs ~"Plan", backend, ~"bug", customer, ~"elasticsearch"
• Adding a label to an epic does not generate a notification ~"Plan", ~"bug", epics, labels, ~"no-priority", ~"no-severity", notifications, ~"portfolio management"
• People can assign weights on any project ~"Plan", ~"bug", issue weight, issues, reproduced on GitLab.com
• When you add an issue to an epic that is already in the epic, you get erroneous system notes ~"Plan", ~"bug", epics, ~"no-priority", ~"no-severity", ~"portfolio management"
• Issue boards with "Upcoming" or "Started" milestones cannot be retrieved via the API ~"Plan", api, auto updated, boards, ~"bug", customer, regression
• Weights editable in board issue side panel ~"Plan", auto updated, boards, ~"bug", issue weight, issues, regression, reproduced on GitLab.com
• Follow-up from "Add presets for navigating Epic Roadmap" ~"Plan", UI polish, ~"bug", ~"no-priority", ~"no-severity", ~"portfolio management", roadmaps, ~"technical debt"
• GitLab Code Search not returning anything while using keyword "version" ~"Plan", ~"bug", customer, ~"elasticsearch"
• Subgroup Issues on board are displayed in both Backlog and their label list ~"Plan", boards, ~"bug", ~"no-priority", ~"no-severity", reproduced on GitLab.com, subgroups

/cc @smcgivern