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](https://github.com/go-gitea/gitea/assets/1666336/4ed884f3-e06a-4862-afd3-3b8aa2488dc6)


![grafik](https://github.com/go-gitea/gitea/assets/1666336/ae6d4981-f252-4f50-a429-04f0f9f1cdf1)


![grafik](https://github.com/go-gitea/gitea/assets/1666336/ca153599-5b0f-4b4a-90fe-18bdfd6f0b6b)

---------

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

models/fixtures/repo_transfer.yml

@@ -5,3 +5,19 @@
   repo_id: 3
   created_unix: 1553610671
   updated_unix: 1553610671
+
+-
+  id: 2
+  doer_id: 16
+  recipient_id: 10
+  repo_id: 21
+  created_unix: 1553610671
+  updated_unix: 1553610671
+
+-
+  id: 3
+  doer_id: 3
+  recipient_id: 10
+  repo_id: 32
+  created_unix: 1553610671
+  updated_unix: 1553610671