[os-zabbix] Zabbix 8.0 has been released

[bastolino]

Important notices
Before you add a new report, we ask you kindly to acknowledge the following:

• I have read the contributing guide lines at https://github.com/opnsense/plugins/blob/master/CONTRIBUTING.md
• I have searched the existing issues, open and closed, and I'm convinced that mine is new.
• When the request is meant for an existing plugin, I've added its name to the title.

Is your feature request related to a problem? Please describe.
As Zabbix 8.0 LTS has been released it'd be nice to also have the respective plugins agent/agent2 and proxy available for opnsense. Created this issue to track progress.

Describe the solution you'd like
Update existing os-zabbixX-agent and os-zabbixX-proxy to Zabbix 8.0

Describe alternatives you've considered
none

Additional context