Add OkHttp as a library used by the core Nomulus project (#2272)

This will be used in a subsequent PR (see #2265) to upload the unavailable
domain names list to the BSA endpoint.

config/dependency-license/allowed_licenses.json

@@ -307,6 +307,16 @@
     },
     {
       "moduleLicense": "The W3C Software License"
+    },
+    {
+      // "Apache License, Version 2.0".
+      "moduleLicense": null,
+      "moduleName": "com.squareup.okhttp3:okhttp"
+    },
+    {
+      // "Apache License, Version 2.0".
+      "moduleLicense": null,
+      "moduleName": "com.squareup.okio:okio"
     }
   ]
 }