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/user_blocking.yml

@@ -0,0 +1,19 @@
+-
+  id: 1
+  blocker_id: 2
+  blockee_id: 29
+
+-
+  id: 2
+  blocker_id: 17
+  blockee_id: 28
+
+-
+  id: 3
+  blocker_id: 2
+  blockee_id: 34
+
+-
+  id: 4
+  blocker_id: 50
+  blockee_id: 34