Add a protection mechanism to prevent accidental deletion of TC

[wxiaoke]

Feature Request

Is your feature request related to a problem? Please describe:

Due to human operation, TC was deleted by mistake

Describe the feature you'd like:

If there are some tips or a second confirmation, it will be better.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

[csuzhangxc]

use deletion validation webhook? like https://github.com/maniSbindra/k8s-delete-validation-webhook

[wxiaoke]

could we integrate the function to tidb operator? I think the reference not fully meet this requirement：When delete CRD，if there are some tips or a second confirmation, it will be better.

[csuzhangxc]

we need to enhance our webhook, https://docs.pingcap.com/tidb-in-kubernetes/stable/enable-admission-webhook