fix: candidate controllers missing Forget call in workqueue

[Revolyssup]

Users encountered the error:

2024-10-02T19:24:30+08:00 [31merror[0m adapter/etcd.go:141 failed to create object, ignore it{error 26 0 rpc error: code = InvalidArgument desc = etcdserver: duplicate key given in txn request} {revision 11 625 <nil>} {key 15 0 /apisix/global_rules/c6bbeaf1 <nil>}

This error only comes for global rule and only comes in candidate controllers.
Reason:
In current logic, the candidate controllers miss the .Forget() call on the successfully processed object and re-add the object in the workqueue. This fix makes sure that event is removed from the queue when object is processed successfully.

How to reproduce the bug:

1. Run make kind-up
2. Modify replica to 3 and apply samples/deploy/composite.yaml
3. Create an ApisixGlobalRule.
4. Check logs of follower pod and there should be error log as shown above.

Steps To Verify fix:

1. make build-image with this commit.
2. Load image in cluster.
3. Run make kind-up
4. Modify replica to 3, modify image to the image created in step 1 and apply samples/deploy/composite.yaml
5. Create an ApisixGlobalRule.
6. Check logs of follower pod and there should be no error log as shown above.