GHSA-5263-pm2h-m7hw Mattermost doesn't restrict which roles can promote a user as system admin

• Go github.com/mattermost/mattermost/server/v8: >= 9.9.0, < 9.9.2 → fixed in 9.9.2 • Go github.com/mattermost/mattermost/server/v8: >= 9.5.0, < 9.5.8 → fixed in 9.5.8 • Go github.com/mattermost/mattermost/server/v8: >= 9.10.0, < 9.10.1 → fixed in 9.10.1 • Go github.com/mattermost/mattermost/server/v8: >= 9.8.0, < 9.8.3 → fixed in 9.8.3

Mattermost versions 9.9.x <= 9.9.1, 9.5.x <= 9.5.7, 9.10.x <= 9.10.0 and 9.8.x <= 9.8.2 fail to restrict which roles can promote a user as system admin which allows a System Role with edit access to the permissions section of system console to update their role (e.g. member) to include the `manage_system` permission, effectively becoming a System Admin.