Order issues in unlabelled triage report by assigned username

Currently the order of usernames in unlabelled triage report are randomised.

It would be easier to scan through the report for each individual's assigned report if they are ordered by usernames.

Example:

`@wlsf82`
 gitlab-org/gitlab#214934 Docs feedback: shfmt section is outdated
 gitlab-org/gitlab#214931 (confidential) ~"(confidential)"

`@mlapierre`
 gitlab-org/gitlab#214930 Gitlab-ci documentation issue
 gitlab-org/gitlab#214922 Allow changing the issue relation ship

`@rymai`
 gitlab-org/gitlab#214921 Don't auto-clear Project URL field when tabbing into it (when creating new projects)
 gitlab-org/gitlab#214918 Problem download latest master artifact return 404 not found

`@niskhakova`
 gitlab-org/gitlab#214917 problem with gitlab-runner on docker
 gitlab-org/gitlab#214915 Make special filters selectable

Can be ordered as

`@mlapierre`
 gitlab-org/gitlab#214930 Gitlab-ci documentation issue
 gitlab-org/gitlab#214922 Allow changing the issue relation ship

`@niskhakova`
 gitlab-org/gitlab#214917 problem with gitlab-runner on docker
 gitlab-org/gitlab#214915 Make special filters selectable

`@rymai`
 gitlab-org/gitlab#214921 Don't auto-clear Project URL field when tabbing into it (when creating new projects)
 gitlab-org/gitlab#214918 Problem download latest master artifact return 404 not found

`@wlsf82`
 gitlab-org/gitlab#214934 Docs feedback: shfmt section is outdated
 gitlab-org/gitlab#214931 (confidential) ~"(confidential)"