Add Dataflow path to generate overall monthly invoice

This forks off the results of the billing_events query from Bigquery and generates the overall invoice for the month.

This also turns the ad hoc beam binary into a proper Nomulus command, allowing us to @Inject from the RegsistryToolComponent and thus template the BillingEvent Bigquery query.

Next steps:
- Add the beam package to the open source build
  - That will likely require updates to the open source jars, since I'm using features from 2.2.0 which was only just released.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=178798943

java/google/registry/tools/BUILD

@@ -36,6 +36,7 @@ java_library(
     visibility = [":allowed-tools"],
     deps = [
         "//java/google/registry/backup",
+        "//java/google/registry/beam",
         "//java/google/registry/bigquery",
         "//java/google/registry/config",
         "//java/google/registry/dns",