Rename 'registry_tool' to 'nomulus'

This changes everything with external visibility beyond the codebase
(i.e. the name of the compiled binary and the documentation that refers
to it). It does not change a lot of things internal to the codebase,
i.e. the "RegistryTool" class didn't change its name. We can rename that
in a subsequent CL if we want to.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135022087

java/google/registry/tools/UniformRapidSuspensionCommand.java

@@ -181,7 +181,7 @@ final class UniformRapidSuspensionCommand extends MutatingEppToolCommand {
       return "";
     }
     StringBuilder undoBuilder = new StringBuilder("UNDO COMMAND:\n\n)")
-        .append("registry_tool -e ")
+        .append("nomulus -e ")
         .append(RegistryToolEnvironment.get())
         .append(" uniform_rapid_suspension --undo --domain_name ")
         .append(domainName);