Manifest webhook silently ignores invalid configuration values

[GeertJohan]

Bug Report

What version of Kubernetes are you using? v1.21.6+k3s1

What version of TiDB Operator are you using? 1.3.8

What did you do? I kubectl apply'd a TidbCluster manifest that has a configuration option which is not supported

What did you expect to see? I expect to get an error, telling me that I used an unsupported or unknown configuration setting.

What did you see instead? The manifest was accepted, but the tikv cluster was not configured as I expected. The configuration setting was silently dropped.

This bug report is not specific to enable-ttl. I suspect that if I had put ttl-check-poll-interval=5s or foobar-nonsense="nonsense" in the config, it would also have been silently ignored.