Add Kubernetes CTS

This adds patches and build specifications for the Kubernetes Conformance Test Suite. This involves
gating various cloud-specific tests behind the providerless flag (otherwise we'd gain a ton of additional dependencies)
and an additional 60MiB in test binary size.
Since the CTS for weird reasons requires kubectl to be available in the path we first build a kubectl go_image and then
stack the CTS on top of it. The output bundle is then preseeded for use.

Test Plan: `bazel run //core/tests/e2e/k8s_cts`

Bug: T836

X-Origin-Diff: phab/D615
GitOrigin-RevId: 7d2cd780a3ffb63b217591c5854b4aec4031d83d
diff --git a/core/tests/e2e/BUILD.bazel b/core/tests/e2e/BUILD.bazel
index 974bcdd..8e74be4 100644
--- a/core/tests/e2e/BUILD.bazel
+++ b/core/tests/e2e/BUILD.bazel
@@ -7,7 +7,7 @@
         "utils.go",
     ],
     importpath = "git.monogon.dev/source/nexantic.git/core/tests/e2e",
-    visibility = ["//visibility:private"],
+    visibility = ["//core/tests:__subpackages__"],
     deps = [
         "//core/proto/api:go_default_library",
         "@io_k8s_api//apps/v1:go_default_library",