Add support for connecting Grafana Cloud via PDC

[ggprod]

Is your feature request related to a problem? Please describe.
Currently to connect Grafana Cloud to Zabbix servers in private VPC requires exposing the Zabbix servers publicly

Describe the solution you'd like
Grafana Cloud has a new PDC (private data connection) capability for connecting to certain data sources. The Zabbix plugin doesn't currently support this option:
https://grafana.com/docs/grafana-cloud/data-configuration/configure-private-datasource-connect/

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[sympatheticmoose]

This might be resolved by #1653