Add user blocking (#29028)

Fixes #17453

This PR adds the abbility to block a user from a personal account or
organization to restrict how the blocked user can interact with the
blocker. The docs explain what's the consequence of blocking a user.

Screenshots:


![grafik](4ed884f3-e06a-4862-afd3-3b8aa2488dc6)


![grafik](ae6d4981-f252-4f50-a429-04f0f9f1cdf1)


![grafik](ca153599-5b0f-4b4a-90fe-18bdfd6f0b6b)

---------

Co-authored-by: Lauris BH <lauris@nix.lv>

services/issue/reaction.go

@@ -0,0 +1,50 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package issue
+
+import (
+	"context"
+
+	issues_model "code.gitea.io/gitea/models/issues"
+	user_model "code.gitea.io/gitea/models/user"
+)
+
+// CreateIssueReaction creates a reaction on an issue.
+func CreateIssueReaction(ctx context.Context, doer *user_model.User, issue *issues_model.Issue, content string) (*issues_model.Reaction, error) {
+	if err := issue.LoadRepo(ctx); err != nil {
+		return nil, err
+	}
+
+	if user_model.IsUserBlockedBy(ctx, doer, issue.PosterID, issue.Repo.OwnerID) {
+		return nil, user_model.ErrBlockedUser
+	}
+
+	return issues_model.CreateReaction(ctx, &issues_model.ReactionOptions{
+		Type:    content,
+		DoerID:  doer.ID,
+		IssueID: issue.ID,
+	})
+}
+
+// CreateCommentReaction creates a reaction on a comment.
+func CreateCommentReaction(ctx context.Context, doer *user_model.User, comment *issues_model.Comment, content string) (*issues_model.Reaction, error) {
+	if err := comment.LoadIssue(ctx); err != nil {
+		return nil, err
+	}
+
+	if err := comment.Issue.LoadRepo(ctx); err != nil {
+		return nil, err
+	}
+
+	if user_model.IsUserBlockedBy(ctx, doer, comment.Issue.PosterID, comment.Issue.Repo.OwnerID, comment.PosterID) {
+		return nil, user_model.ErrBlockedUser
+	}
+
+	return issues_model.CreateReaction(ctx, &issues_model.ReactionOptions{
+		Type:      content,
+		DoerID:    doer.ID,
+		IssueID:   comment.Issue.ID,
+		CommentID: comment.ID,
+	})
+}