Fix CODEOWNERS review request attribution using comment metadata (#36348)

Fixes #36333

## Problem

When CODEOWNERS automatically assigns reviewers to a pull request, the
timeline incorrectly shows the PR author as the one who requested the
review (e.g., "PR_AUTHOR requested review from CODE_OWNER"). This is
misleading since the action was triggered automatically by CODEOWNERS
rules, not by the PR author.

## Solution

Store CODEOWNERS attribution in comment metadata instead of changing the
doer user:
- Add `SpecialDoerName` field to `CommentMetaData` struct (value:
`"CODEOWNERS"` for CODEOWNERS-triggered requests)
- Pass `isCodeOwners=true` to `AddReviewRequest` and
`AddTeamReviewRequest` functions
- Template can check this metadata to show appropriate attribution
message

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/issue/assignee.go

@@ -70,7 +70,7 @@ func ReviewRequest(ctx context.Context, issue *issues_model.Issue, doer *user_mo
 	}
 
 	if isAdd {
-		comment, err = issues_model.AddReviewRequest(ctx, issue, reviewer, doer)
+		comment, err = issues_model.AddReviewRequest(ctx, issue, reviewer, doer, false)
 	} else {
 		comment, err = issues_model.RemoveReviewRequest(ctx, issue, reviewer, doer)
 	}
@@ -224,7 +224,7 @@ func TeamReviewRequest(ctx context.Context, issue *issues_model.Issue, doer *use
 		return nil, err
 	}
 	if isAdd {
-		comment, err = issues_model.AddTeamReviewRequest(ctx, issue, reviewer, doer)
+		comment, err = issues_model.AddTeamReviewRequest(ctx, issue, reviewer, doer, false)
 	} else {
 		comment, err = issues_model.RemoveTeamReviewRequest(ctx, issue, reviewer, doer)
 	}