Add Visible modes function from Organisation to Users too (#16069)

You can limit or hide organisations. This pull make it also posible for users

- new strings to translte
- add checkbox to user profile form
- add checkbox to admin user.edit form
- filter explore page user search
- filter api admin and public user searches
- allow admins view "hidden" users
- add app option DEFAULT_USER_VISIBILITY
- rewrite many files to use Visibility field
- check for teams intersection
- fix context output
- right fake 404 if not visible

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Andrew Thornton <art27@cantab.net>

templates/swagger/v1_json.tmpl

@@ -13334,6 +13334,10 @@
         "username": {
           "type": "string",
           "x-go-name": "Username"
+        },
+        "visibility": {
+          "type": "string",
+          "x-go-name": "Visibility"
         }
       },
       "x-go-package": "code.gitea.io/gitea/modules/structs"
@@ -14143,6 +14147,10 @@
           "format": "int64",
           "x-go-name": "SourceID"
         },
+        "visibility": {
+          "type": "string",
+          "x-go-name": "Visibility"
+        },
         "website": {
           "type": "string",
           "x-go-name": "Website"
@@ -16637,6 +16645,11 @@
           "format": "int64",
           "x-go-name": "StarredRepos"
         },
+        "visibility": {
+          "description": "User visibility level option: public, limited, private",
+          "type": "string",
+          "x-go-name": "Visibility"
+        },
         "website": {
           "description": "the user's website",
           "type": "string",