replace hardcoded GT and LT with CommandKeyword enum (#3079)

Author: minwoo1999

Diff for: src/main/java/io/lettuce/core/ZAddArgs.java

@@ -182,11 +182,11 @@ public <K, V> void build(CommandArgs<K, V> args) {
         }
 
         if (gt) {
-            args.add("GT");
+            args.add(GT);
         }
 
         if (lt) {
-            args.add("LT");
+            args.add(LT);
         }
 
         if (ch) {

Diff for: src/main/java/io/lettuce/core/protocol/CommandKeyword.java

@@ -49,7 +49,7 @@ public enum CommandKeyword implements ProtocolKeyword {
 
     MIGRATING, IMPORTING, SAVE, SKIPME, SLAVES, STREAM, STORE, SUM, SEGFAULT, SETUSER, TAKEOVER, TRACKING, TRACKINGINFO, TYPE, UNBLOCK, USERS, USAGE, WEIGHTS, WHOAMI,
 
-    WITHMATCHLEN, WITHSCORE, WITHSCORES, WITHVALUES, XOR, XX, YES, INDENT, NEWLINE, SPACE;
+    WITHMATCHLEN, WITHSCORE, WITHSCORES, WITHVALUES, XOR, XX, YES, INDENT, NEWLINE, SPACE, GT, LT;
 
     public final byte[] bytes;