metropolis: unify utility packages

One last sweeping rename / reshuffle.

We get rid of //metropolis/node/common and //golibs, unifying them into
a single //metropolis/pkg meta-package.

This is to be documented somwhere properly, but here's the new logic
behind selecting where to place a new library package:

 - if it's specific to k8s-on-metropolis, put it in
   //metropolis/node/kubernetes/*. This is a self-contained tree that
   other paths cannot import from.
 - if it's a big new subsystem of the metropolis core, put it in
   //metropolis/node/core. This can be imported by anything in
   //m/n (eg the Kubernetes code at //m/n/kubernetes
 - otherwise, treat it as generic library that's part of the metropolis
   project, and put it in //metropolis/pkg. This can be imported by
   anything within //metropolis.

This will be followed up by a diff that updates visibility rules.

Test Plan: Pure refactor, CI only.

X-Origin-Diff: phab/D683
GitOrigin-RevId: 883e7f09a7d22d64e966d07bbe839454ed081c79
diff --git a/metropolis/node/kubernetes/reconciler/BUILD.bazel b/metropolis/node/kubernetes/reconciler/BUILD.bazel
index d8f2db6..e4d4f17 100644
--- a/metropolis/node/kubernetes/reconciler/BUILD.bazel
+++ b/metropolis/node/kubernetes/reconciler/BUILD.bazel
@@ -13,7 +13,7 @@
     importpath = "git.monogon.dev/source/nexantic.git/metropolis/node/kubernetes/reconciler",
     visibility = ["//metropolis/node:__subpackages__"],
     deps = [
-        "//metropolis/node/common/supervisor:go_default_library",
+        "//metropolis/pkg/supervisor:go_default_library",
         "@io_k8s_api//core/v1:go_default_library",
         "@io_k8s_api//node/v1beta1:go_default_library",
         "@io_k8s_api//policy/v1beta1:go_default_library",