Allow Custom Netpols for Prometheus Stack Package

[joelmccoy]

Is your feature request related to a problem? Please describe.

Currently, alertmanager can't reach outside the monitoring namespace with the default netpols deployed with core. This is a problem, because it is typical to setup alertmanager with some sort of notification system (i.e. slack, email, etc). Currently there is no way to route this traffic out of alertmanager. And since each destination is going to be different for each customer, it makes sense to allow them to configure this themselves. Recommend we add a custom value that can be overriden and allows netpols for unanticipated scenarios

Describe the solution you'd like

• Given a deploy of uds-core
• When a user specifies an override value to add a custom netpol to the prometheus-stack package to allow alertmanager traffic to their end destination
• Then alertmanager is able to properly send alerts to their notification system

Describe alternatives you've considered

• Deploy a custom package with a single netpol manifest in it (feels overkill to create a package for this single use case that could be override-able with a value)
• Set a blanket allow alertmanager egress to everywhere (probably not the best for security reasons)

Additional context

Originally mentioned this in a comment here, but feel that this is a different problem and merits it's own issue

[joelmccoy]

Looks to be a duplicate / subset of #951