DNS optimization

Created by: live77

What type of PR is this?

/kind feature

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #1951 (closed)

Special notes for reviewers:

Does this PR introduced a user-facing change?

DNS optimization for ks-console 
- Use ks-apiserver Service Name directly instead of ks-apiserver.kubesphere-system.svc as API's URL.
- Add a DNS cache plugin to caching the DNS results (dnscache)

Additional documentation, usage docs, etc.:

1. Use ks-apiserver instead of ks-apiserver.kubesphere-system.svc to speedup dns lookup. (first query hit) below screenshot proves, after using ks-apiserver, the first dns lookup got the answer.

2. Use dnscache module to enable local dns cache on the console server side. below screenshot shows the cache hit result, it works.