go/mirko: add SQL migrations machinery

This uses github.com/golang-migrate/migrate and adds a Source that
allows using go_embed data files.

We also provide a test/example.

Change-Id: Icd2b6c7f7d0f728073b3fdf39b432b33ce61a3cd
diff --git a/go/mirko/BUILD.bazel b/go/mirko/BUILD.bazel
index 89b40ed..405987e 100644
--- a/go/mirko/BUILD.bazel
+++ b/go/mirko/BUILD.bazel
@@ -5,13 +5,16 @@
     srcs = [
         "kubernetes.go",
         "mirko.go",
+        "sql_migrations.go",
     ],
     importpath = "code.hackerspace.pl/hscloud/go/mirko",
     visibility = ["//visibility:public"],
     deps = [
         "//go/pki:go_default_library",
         "//go/statusz:go_default_library",
+        "@com_github_gchaincl_sqlhooks//:go_default_library",
         "@com_github_golang_glog//:go_default_library",
+        "@com_github_golang_migrate_migrate_v4//source:go_default_library",
         "@io_k8s_client_go//kubernetes:go_default_library",
         "@io_k8s_client_go//rest:go_default_library",
         "@org_golang_google_grpc//:go_default_library",