m/c/metroctl: add skeleton and dependencies

This adds the skeleton for the Metropolis control command line,
metroctl. It currently consists of a single root command doing nothing
and the dependency updates for viper, the library providing command
line parsing and completion support.
Actual functionality will be in subsequent CLs.

Change-Id: I73d0e2956d9550902a80295928e94cb32bb12cfc
Reviewed-on: https://review.monogon.dev/c/monogon/+/337
Reviewed-by: Sergiusz Bazanski <serge@monogon.tech>
diff --git a/metropolis/cli/metroctl/BUILD.bazel b/metropolis/cli/metroctl/BUILD.bazel
new file mode 100644
index 0000000..154fba1
--- /dev/null
+++ b/metropolis/cli/metroctl/BUILD.bazel
@@ -0,0 +1,15 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["main.go"],
+    importpath = "source.monogon.dev/metropolis/cli/metroctl",
+    visibility = ["//visibility:private"],
+    deps = ["@com_github_spf13_cobra//:go_default_library"],
+)
+
+go_binary(
+    name = "metroctl",
+    embed = [":go_default_library"],
+    visibility = ["//visibility:public"],
+)