Add nomulus count_domains command

This efficiently counts domains without having to load them (as opposed to the
existing list_domains command which does load then).

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=194559095

java/google/registry/tools/RegistryTool.java

@@ -36,6 +36,7 @@ public final class RegistryTool {
           .put("check_domain_fee", CheckDomainFeeCommand.class)
           .put("check_snapshot", CheckSnapshotCommand.class)
           .put("convert_idn", ConvertIdnCommand.class)
+          .put("count_domains", CountDomainsCommand.class)
           .put("create_anchor_tenant", CreateAnchorTenantCommand.class)
           .put("create_auction_credits", CreateAuctionCreditsCommand.class)
           .put("create_cdns_tld", CreateCdnsTld.class)