Support annotations in targets ingress resources

[nickytd]

What this PR does

This PR adds support for adding annotations to target ingresses.

Following example illustrates adding annotations to a grafana target, leveraging the default cert-manager and dns-manager extensions in gardener shoot clusters. Once the ingresses are annorated the respective extensions take over the lifecycle of the dns records and server-side certificates of the expose ingress.

ingress:
  create: true
  ingressClassName: nginx
  annotations:
    cert.gardener.cloud/purpose: managed
    dns.gardener.cloud/class: garden
    dns.gardener.cloud/dnsnames: "*"
    dns.gardener.cloud/ttl: "600"
    nginx.ingress.kubernetes.io/force-ssl-redirect: "true"
  tlsSecretRef:
    name: "grafana-tls"

oidc-apps-controller now supports specifying annotations for the target ingresses