CDC print lots of "etcd client outCh blocking too long, the etcdWorker may be stuck" and checkpoint lag metric abnormal

[fubinzh]

What did you do?

1. create cdc changefeed
2. run workload (use lighting tidb backend to import 10+ tables )

What did you expect to see?

CDC should be normal.

What did you see instead?

CDC print lots of WARN :
{"container":"ticdc","namespace":"cdc-testbed-tps-7653796-1-407","pod":"upstream-ticdc-0","log":"[client.go:272] ["etcd client outCh blocking too long, the etcdWorker may be stuck"] [duration=5m32.997091037s] [role=owner]","level":"WARN"}

CDC checkpoint lag abnormal:

Versions of the cluster

cdc version: master, git-hash: 4538839

[flowbehappy]

Introduces by #11830

[fubinzh]

/severity major

[fubinzh]

/type regression

[wlwilliamx]

/affects 6.5 7.1 7.5 8.1 8.5