Add a new check API that does not wrap the domain check EPP flow

Copied class and test from CheckApiAction. All unit tests passing.

Remaining work: add metrics

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=198916177

java/google/registry/env/common/pubapi/WEB-INF/web.xml

@@ -37,6 +37,15 @@
     <url-pattern>/check</url-pattern>
   </servlet-mapping>
 
+  <!--
+      Temporary end point for new implementation of availability checks
+      TODO(b/80417678): remove this stanza
+   -->
+  <servlet-mapping>
+    <servlet-name>pubapi-servlet</servlet-name>
+    <url-pattern>/check2</url-pattern>
+  </servlet-mapping>
+
   <!-- Security config -->
   <security-constraint>
     <web-resource-collection>