Add "pubapi" App Engine service for check API, WHOIS, and RDAP

The migration plan is as follows:
1. This CL, which adds the new "pubapi" service that serves the check API, WHOIS, and RDAP.
2a. Update our public facing sites to switch over to use the new service.
2b. (either order) Rewrite the check API to remove dependencies on flows.
3. ... eventually, once the frontend service is no longer being hit by this traffic, remove its handling of these public endpoints.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=197716346

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

@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
+
+  <application>domain-registry</application>
+  <version>1</version>
+  <runtime>java8</runtime>
+  <module>pubapi</module>
+  <threadsafe>true</threadsafe>
+  <sessions-enabled>true</sessions-enabled>
+  <instance-class>B4</instance-class>
+  <basic-scaling>
+    <max-instances>8</max-instances>
+    <idle-timeout>10m</idle-timeout>
+  </basic-scaling>
+
+  <system-properties>
+    <property name="java.util.logging.config.file"
+              value="WEB-INF/logging.properties"/>
+    <property name="google.registry.environment"
+              value="crash"/>
+  </system-properties>
+
+  <static-files>
+    <include path="/*.html" expiration="1m"/>
+    <include path="/assets/js/**" expiration="1m"/>
+    <include path="/assets/css/**" expiration="1m"/>
+    <include path="/assets/images/**" expiration="1m"/>
+  </static-files>
+</appengine-web-app>