Decouple HookTask from Repository (#17940)

At the moment a repository reference is needed for webhooks. With the
upcoming package PR we need to send webhooks without a repository
reference. For example a package is uploaded to an organization. In
theory this enables the usage of webhooks for future user actions.

This PR removes the repository id from `HookTask` and changes how the
hooks are processed (see `services/webhook/deliver.go`). In a follow up
PR I want to remove the usage of the `UniqueQueue´ and replace it with a
normal queue because there is no reason to be unique.

Co-authored-by: 6543 <6543@obermui.de>

routers/api/v1/repo/hook_test.go

@@ -28,7 +28,6 @@ func TestTestHook(t *testing.T) {
 	assert.EqualValues(t, http.StatusNoContent, ctx.Resp.Status())
 
 	unittest.AssertExistsAndLoadBean(t, &webhook.HookTask{
-		RepoID: 1,
 		HookID: 1,
 	}, unittest.Cond("is_delivered=?", false))
 }