Change externalElasticsearchUrl to externalElasticsearchHost at cc

Created by: mangoGoForward

What this PR dose?

Change externalElasticsearchUrl to externalElasticsearchHost at cc, and make the definition more clear.

What this PR does / why we need it:

please see kubesphere#3829 (closed).

Which issue(s) this PR fixes:

Fixes kubesphere#3829 (closed) .