cmd/k8s-operator/e2e: add egress tests (#20648)

Add end-to-end tests for egress to a tailnet target via its FQDN, IPv4 and
IPv6 addresses.

Update the kind cluster used in tests to support dual-stack (to allow
testing egress to both IPv4 and IPv6 tailnet targets). For pre-existing
clusters, detect on test setup which IP families the cluster supports.
IPv4/IPv6 subtests are skipped if not supported.

Run the end-to-end tests in parallel to improve the speed of test runs. To
enable this, run TestProxyGroupPolicy in a dedicated namespace so its
ValidatingAdmissionPolicies don't affect other parallel tests sharing the
same namespace.

Updates tailscale/corp#34834

Signed-off-by: Becky Pauley <becky@tailscale.com>