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>

tests/integration/api_repo_collaborator_test.go

@@ -27,6 +27,7 @@ func TestAPIRepoCollaboratorPermission(t *testing.T) {
 		user5 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 5})
 		user10 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 10})
 		user11 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 11})
+		user34 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 34})
 
 		testCtx := NewAPITestContext(t, repo2Owner.Name, repo2.Name, auth_model.AccessTokenScopeWriteRepository)
 
@@ -86,6 +87,12 @@ func TestAPIRepoCollaboratorPermission(t *testing.T) {
 			MakeRequest(t, req, http.StatusNotFound)
 		})
 
+		t.Run("CollaboratorBlocked", func(t *testing.T) {
+			ctx := NewAPITestContext(t, repo2Owner.Name, repo2.Name, auth_model.AccessTokenScopeWriteRepository)
+			ctx.ExpectedCode = http.StatusForbidden
+			doAPIAddCollaborator(ctx, user34.Name, perm.AccessModeAdmin)(t)
+		})
+
 		t.Run("CollaboratorCanQueryItsPermissions", func(t *testing.T) {
 			t.Run("AddUserAsCollaboratorWithReadAccess", doAPIAddCollaborator(testCtx, user5.Name, perm.AccessModeRead))