refactor(source/istio): add transformers

[ivankatliarchuk]

What does it do ?

Reduce memory footprint for service kinds in istio sources. Similar solution to #5596, with difference that trying to work out a framework that could be used accross multiple kube object kinds

Follow-up:

• remove this logic

  external-dns/source/istio_gateway.go

  Line 195 in bb7a8af

  for _, ep := range endpoints {

  instead do target sorting here

  external-dns/endpoint/endpoint.go

  Line 252 in bb7a8af

  func NewEndpointWithTTL(dnsName, recordType string, ttl TTL, targets ...string) *Endpoint {

  . Most likely few more unit tests required
• Review duplicated logic in istio

  external-dns/source/istio_gateway.go

  Line 233 in bb7a8af

  func (sc *gatewaySource) targetsFromIngress(ctx context.Context, ingressStr string, gateway *networkingv1beta1.Gateway) (endpoint.Targets, error) {

  and istio_virtualservice

  external-dns/source/istio_virtualservice.go

  Line 420 in bb7a8af

  func (sc *virtualServiceSource) targetsFromIngress(ctx context.Context, ingressStr string, gateway *v1beta1.Gateway) (endpoint.Targets, error) {

  . There are 2 issues
  1. Kube API call on each run sc.kubeClient.NetworkingV1().Ingresses(namespace).Get(ctx, name, metav1.GetOptions{})
  2. When istio and istio_virtualservice enabled, the same logic is executed twice, and then wrapper dedupsource removes duplicates. This is super inneficient, as same logic executed in both sources
  3. FQDN Templating, with kube transfomers, we could execute FQDN during the entity is added to the infromer cache. This has one major advantage, execute FQDN once on entity added vs execute FQDN every time the Endpoint method executes.

Motivation

Slicing PR #5708
Relates: #5595

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

[ivankatliarchuk]

/retest

[mloiseleur]

/lgtm

[ivankatliarchuk]

/approve

[k8s-ci-robot]

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