c/bmaas/bmdb: implement OS installation flow

This adds two new tags: OSInstallationRequest and
OSInstallationResponse. It also implements interacting with these tags
from the agent side.

This doesn't yet implement any admin/user-facing API to actually request
OS installation, for now we just exercise this in tests.

Change-Id: I2e31a8369a3a8670bb92bcacfb8231a0d5e1b9fd
Reviewed-on: https://review.monogon.dev/c/monogon/+/1011
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
Tested-by: Jenkins CI
diff --git a/cloud/bmaas/server/BUILD.bazel b/cloud/bmaas/server/BUILD.bazel
index ee491d1..2c96a03 100644
--- a/cloud/bmaas/server/BUILD.bazel
+++ b/cloud/bmaas/server/BUILD.bazel
@@ -40,5 +40,6 @@
         "//metropolis/node/core/rpc",
         "@com_github_google_uuid//:uuid",
         "@org_golang_google_grpc//:go_default_library",
+        "@org_golang_google_protobuf//proto",
     ],
 )