Include resource state events in Gitlab downloads (#29382)

Some specific events on Gitlab issues and merge requests are stored
separately from comments as "resource state events". With this change,
all relevant resource state events are downloaded during issue and merge
request migration, and converted to comments.

This PR also updates the template used to render comments to add support
for migrated comments of these types.

ref: https://docs.gitlab.com/ee/api/resource_state_events.html

services/migrations/gitlab.go

@@ -517,6 +517,60 @@ func (g *GitlabDownloader) GetComments(commentable base.Commentable) ([]*base.Co
 		}
 		page = resp.NextPage
 	}
+
+	page = 1
+	for {
+		var stateEvents []*gitlab.StateEvent
+		var resp *gitlab.Response
+		var err error
+		if context.IsMergeRequest {
+			stateEvents, resp, err = g.client.ResourceStateEvents.ListMergeStateEvents(g.repoID, int(commentable.GetForeignIndex()), &gitlab.ListStateEventsOptions{
+				ListOptions: gitlab.ListOptions{
+					Page:    page,
+					PerPage: g.maxPerPage,
+				},
+			}, nil, gitlab.WithContext(g.ctx))
+		} else {
+			stateEvents, resp, err = g.client.ResourceStateEvents.ListIssueStateEvents(g.repoID, int(commentable.GetForeignIndex()), &gitlab.ListStateEventsOptions{
+				ListOptions: gitlab.ListOptions{
+					Page:    page,
+					PerPage: g.maxPerPage,
+				},
+			}, nil, gitlab.WithContext(g.ctx))
+		}
+		if err != nil {
+			return nil, false, fmt.Errorf("error while listing state events: %v %w", g.repoID, err)
+		}
+
+		for _, stateEvent := range stateEvents {
+			comment := &base.Comment{
+				IssueIndex: commentable.GetLocalIndex(),
+				Index:      int64(stateEvent.ID),
+				PosterID:   int64(stateEvent.User.ID),
+				PosterName: stateEvent.User.Username,
+				Content:    "",
+				Created:    *stateEvent.CreatedAt,
+			}
+			switch stateEvent.State {
+			case gitlab.ClosedEventType:
+				comment.CommentType = issues_model.CommentTypeClose.String()
+			case gitlab.MergedEventType:
+				comment.CommentType = issues_model.CommentTypeMergePull.String()
+			case gitlab.ReopenedEventType:
+				comment.CommentType = issues_model.CommentTypeReopen.String()
+			default:
+				// Ignore other event types
+				continue
+			}
+			allComments = append(allComments, comment)
+		}
+
+		if resp.NextPage == 0 {
+			break
+		}
+		page = resp.NextPage
+	}
+
 	return allComments, true, nil
 }