feat(ui): add links to assigners in issue comments (#8264)

When a user is assigning an issue or PR to another user, an entry is posted in the issue comment list. This PR adds a link to the one assigning the issue. Additionally, tests for preventing XSS vulnerabilities in label rendering were added.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8264
Reviewed-by: Gusted <gusted@noreply.codeberg.org>

models/fixtures/label.yml

@@ -3,6 +3,7 @@
   repo_id: 1
   org_id: 0
   name: label1
+  description: 'First label'
   color: '#abcdef'
   exclusive: false
   num_issues: 2
@@ -107,3 +108,26 @@
   num_issues: 0
   num_closed_issues: 0
   archived_unix: 0
+
+-
+  id: 11
+  repo_id: 3
+  org_id: 0
+  name: "  <script>malicious</script> /'?&"
+  description: "Malicious label ' <script>malicious</script>"
+  color: '#000000'
+  exclusive: true
+  num_issues: 0
+  num_closed_issues: 0
+  archived_unix: 0
+
+-
+  id: 12
+  repo_id: 3
+  org_id: 0
+  name: 'archived label<>'
+  color: '#000000'
+  exclusive: false
+  num_issues: 0
+  num_closed_issues: 0
+  archived_unix: 2991092130