Ip zbx name

[ozhuang]

What this PR does / why we need it:

1. Added ClusterIP as an option for all services.

2. Use unique zabbix agent hostname in both pods (zabbix server & zabbix proxy), to avoid duplicate zabbix agent hostname on Zabbix frontend.

   • Agent in server pod will use the default "Zabbix server" name displayed on frontend.
   • Agent in proxy pod will use the pod name, eg: "zabbix-zabbix-proxy-0".
   • zabbixagent.ZBX_HOSTNAME variable is removed to achieve this.

Which issue this PR fixes

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [x] DCO signed
• [x] Chart Version bumped
• [x] Variables are documented in the README.md