[helm] Parameterize the DNS egress NetworkPolicy

[lindhe]

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

The DNS egress NetwrokPolicy is using a hard-coded port name, dns:

loki/production/helm/loki/templates/networkpolicy.yaml

Line 38 in 2c5eabd

- port: dns

This is incompatible with some environments, for example the coredns installation used by RKE2 by default (it has port names udp-53 and tcp-53).

Describe the solution you'd like

I suggest we make this configurable via Helm values.

Describe alternatives you've considered

As a work-around, I'll be using Kustomize to edit the NetworkPolicy object. Another alternative would be to create a new NetworkPolicy manually.

Additional context

Additionally, the NetworkPolicy also has a hard-coded namespaceSelector:

loki/production/helm/loki/templates/networkpolicy.yaml

Line 41 in 2c5eabd

- namespaceSelector: {}

I suggest we make that configurable as well, for similar reasons (and also for the security minded folks that want to restrict network policies even further).

I'm happy to help implement this!