Add EROFS creation utility and Bazel rule

This adds a binary which can create EROFS filesystems from a spec and a Bazel rule similar to
node_initramfs which creates EROFS filesystems.

Test Plan: Tested in subsequent revision

X-Origin-Diff: phab/D695
GitOrigin-RevId: 4e8f970938c93606da46f475387de1e013b1c35c
diff --git a/metropolis/node/build/mkerofs/BUILD.bazel b/metropolis/node/build/mkerofs/BUILD.bazel
new file mode 100644
index 0000000..6de1c73
--- /dev/null
+++ b/metropolis/node/build/mkerofs/BUILD.bazel
@@ -0,0 +1,19 @@
+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/node/build/mkerofs",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//metropolis/node/build/mkerofs/fsspec:go_default_library",
+        "//metropolis/pkg/erofs:go_default_library",
+        "@com_github_golang_protobuf//proto:go_default_library",
+    ],
+)
+
+go_binary(
+    name = "mkerofs",
+    embed = [":go_default_library"],
+    visibility = ["//visibility:public"],
+)