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/collaboration.yml

@@ -51,3 +51,15 @@
   repo_id: 60
   user_id: 38
   mode: 2 # write
+
+-
+  id: 10
+  repo_id: 21
+  user_id: 10
+  mode: 2 # write
+
+-
+  id: 11
+  repo_id: 32
+  user_id: 10
+  mode: 2 # write