Add a Nomulus command to list Datastore operations

Command would be useful when checking the status of daily
backup jobs.

Only two modes are supported: list all operations, or list those
that started within the past period as specified by command line
option.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=229239783

java/google/registry/tools/RegistryTool.java

@@ -79,6 +79,7 @@ public final class RegistryTool {
           .put("hash_certificate", HashCertificateCommand.class)
           .put("import_datastore", ImportDatastoreCommand.class)
           .put("list_cursors", ListCursorsCommand.class)
+          .put("list_datastore_operations", ListDatastoreOperationsCommand.class)
           .put("list_domains", ListDomainsCommand.class)
           .put("list_hosts", ListHostsCommand.class)
           .put("list_premium_lists", ListPremiumListsCommand.class)