Add SetNumInstancesCommand in Nomulus tool to adjust the number of instances

for a given service and version at runtime.

Note that this CL only supports the adjustment for a given service and version. I will add another functionality to let this command be able to detect all non-live versions automatically and apply the adjustment.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=221092001

java/google/registry/tools/RegistryTool.java

@@ -104,6 +104,7 @@ public final class RegistryTool {
           .put("resave_environment_entities", ResaveEnvironmentEntitiesCommand.class)
           .put("resave_epp_resource", ResaveEppResourceCommand.class)
           .put("send_escrow_report_to_icann", SendEscrowReportToIcannCommand.class)
+          .put("set_num_instances", SetNumInstancesCommand.class)
           .put("setup_ote", SetupOteCommand.class)
           .put("uniform_rapid_suspension", UniformRapidSuspensionCommand.class)
           .put("unlock_domain", UnlockDomainCommand.class)