go/net/tinylb: init

This implements tinylb, a tiny round-robin load balancer for
net.Conn/net.Listener protocols.

This will be used to loadbalance connections to Kubernetes apiservers
before cluster networking is available.

Change-Id: I48892e1fe03e0648df60c674e7394ca69b32932d
Reviewed-on: https://review.monogon.dev/c/monogon/+/1369
Tested-by: Jenkins CI
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/metropolis/pkg/supervisor/BUILD.bazel b/metropolis/pkg/supervisor/BUILD.bazel
index d096c5d..a12de83 100644
--- a/metropolis/pkg/supervisor/BUILD.bazel
+++ b/metropolis/pkg/supervisor/BUILD.bazel
@@ -10,7 +10,11 @@
         "supervisor_testhelpers.go",
     ],
     importpath = "source.monogon.dev/metropolis/pkg/supervisor",
-    visibility = ["//metropolis:__subpackages__"],
+    visibility = [
+        "//metropolis:__subpackages__",
+        # TODO(q3k): move supervisor to //go
+        "//go:__subpackages__",
+    ],
     deps = [
         "//metropolis/pkg/logtree",
         "@com_github_cenkalti_backoff_v4//:backoff",