Add apache beam to registry and open source

This is the initial commit of the new billing system, rewritten as an Apache
Beam pipeline. This contains a basic end-to-end pipeline as proof of concept,
and boilerplate for GenerateInvoicesAction, which will eventually be our
automated invoice generation endpoint.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=174184171

java/google/registry/module/backend/BUILD

@@ -11,6 +11,7 @@ java_library(
         "//java/google/registry/backup",
         "//java/google/registry/batch",
         "//java/google/registry/bigquery",
+        "//java/google/registry/billing",
         "//java/google/registry/config",
         "//java/google/registry/cron",
         "//java/google/registry/dns",

java/google/registry/module/backend/BackendRequestComponent.java

@@ -28,6 +28,7 @@ import google.registry.batch.MapreduceEntityCleanupAction;
 import google.registry.batch.RefreshDnsOnHostRenameAction;
 import google.registry.batch.ResaveAllEppResourcesAction;
 import google.registry.batch.VerifyEntityIntegrityAction;
+import google.registry.billing.GenerateInvoicesAction;
 import google.registry.cron.CommitLogFanoutAction;
 import google.registry.cron.CronModule;
 import google.registry.cron.TldFanoutAction;
@@ -114,6 +115,7 @@ interface BackendRequestComponent {
   ExportDomainListsAction exportDomainListsAction();
   ExportReservedTermsAction exportReservedTermsAction();
   ExportSnapshotAction exportSnapshotAction();
+  GenerateInvoicesAction generateInvoicesAction();
   IcannReportingStagingAction icannReportingStagingAction();
   IcannReportingUploadAction icannReportingUploadAction();
   LoadSnapshotAction loadSnapshotAction();