Derive RDAP link paths from the received query

The former method -- a config string -- was cumbersome, as each Nomulus system would have to configure the link base to its own URL.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=173567021

java/google/registry/rdap/RdapJsonFormatter.java

@@ -410,8 +410,14 @@ public class RdapJsonFormatter {
     if (parameters.getTypeString() != null) {
       jsonBuilder.put("typeString", parameters.getTypeString());
     }
+    String linkBaseNotNull = nullToEmpty(linkBase);
+    String linkValueSuffixNotNull = nullToEmpty(parameters.getLinkValueSuffix());
     String linkValueString =
-        nullToEmpty(linkBase) + nullToEmpty(parameters.getLinkValueSuffix());
+        String.format(
+            "%s%s%s",
+            linkBaseNotNull,
+            (linkBaseNotNull.endsWith("/") || linkValueSuffixNotNull.startsWith("/")) ? "" : "/",
+            linkValueSuffixNotNull);
     if (parameters.getLinkHrefUrlString() == null) {
       jsonBuilder.put("links", ImmutableList.of(ImmutableMap.of(
           "value", linkValueString,