feat: Opt-in to endpoints for Load balancer Services

[jonstacks]

What

Overview

ngrok is migrating from Edges to Endpoints. This allows users to opt-in to using endpoints instead of edges for Load Balancer Services by adding the annotation k8s.ngrok.com/use-endpoints: "true" (in most cases).

Potential Rough Edges (Running List)

A few cases that notable cases where this migration isn't perfect and could use more consideration or changes:

1. TLS Edges default to terminating TLS at the ngrok edge. Cloud Endpoints with urls that look like tls://<domain> do not terminate TLS by default and need to supply a terminate-tls traffic policy action if they want TLS to be terminated at ngrok.
   There are a few workarounds for this, but if you are already using modulesets you can create the following moduleset and specify a min version for TLS termination. As part of the transparent migration from modulesets -> trafficpolicy when using endpoints, this will instruct it to terminate TLS. Ex:

apiVersion: ingress.k8s.ngrok.com/v1alpha1
kind: NgrokModuleSet
metadata:
  name: tls
  namespace: default
modules:
  tlsTermination:
    minVersion: "1.2"

Then you just need to make sure to add the the tls NgrokModuleSet to the list of modules on a service, like so:

apiVersion: v1
kind: Service
metadata:
  annotations:
    k8s.ngrok.com/modules: only-trusted-ips, tls
    k8s.ngrok.com/use-endpoints: "true"

2. Note: We are missing equivalent traffic policy actions for SAML, OIDC, and oAuth modules.

How

This change allows users to opt-in to using endpoints instead of edges. There is a slight refactor for the different types of "resolvers" to their own package so that we can use those resolvers in the util package without creating circular dependencies.

The current design is if the k8s.ngrok.com/use-endpoints: "true" annotation is present, it will attempt to transparently convert the modulesets from the modulesets annotation to equivalent traffic policy. If that fails because we don't have support for a given module in traffic policy or the annotation does not exist, it will fall back to using edges for minimal impact.

Breaking Changes

No, there should not be any breaking changes. All of this work outside of the refactor is hidden behind an opt-in annotation.