Enable/disable owner and repo projects independently (#28805)

Part of #23318 

Add menu in repo settings to allow for repo admin to decide not just if
projects are enabled or disabled per repo, but also which kind of
projects (repo-level/owner-level) are enabled. If repo projects
disabled, don't show the projects tab.


![grafik](https://github.com/go-gitea/gitea/assets/47871822/b9b43fb4-824b-47f9-b8e2-12004313647c)

---------

Co-authored-by: delvh <dev.lh@web.de>

models/fixtures/repo_unit.yml

@@ -520,6 +520,7 @@
   id: 75
   repo_id: 1
   type: 8
+  config: "{\"ProjectsMode\":\"all\"}"
   created_unix: 946684810
 
 -
@@ -650,12 +651,6 @@
   type: 2
   created_unix: 946684810
 
--
-  id: 98
-  repo_id: 1
-  type: 8
-  created_unix: 946684810
-
 -
   id: 99
   repo_id: 1