Fix antlr4 parser issues (#1094)

* Fix antlr4 parser issues

Signed-off-by: Lantao Jin <ltjin@amazon.com>

* Case insensitive lexer

Signed-off-by: Lantao Jin <ltjin@amazon.com>

* revert useless change

Signed-off-by: Lantao Jin <ltjin@amazon.com>

* remove tokens file

Signed-off-by: Lantao Jin <ltjin@amazon.com>

---------

Signed-off-by: Lantao Jin <ltjin@amazon.com>

Author: LantaoJin

ppl-spark-integration/src/main/antlr4/OpenSearchPPLLexer.g4

@@ -7,7 +7,7 @@
 lexer grammar OpenSearchPPLLexer;
 
 channels { WHITESPACE, ERRORCHANNEL }
-
+options { caseInsensitive = true; }
 
 // COMMAND KEYWORDS
 SEARCH:                             'SEARCH';

ppl-spark-integration/src/main/antlr4/OpenSearchPPLParser.g4

@@ -1115,7 +1115,11 @@ keywordsCanBeId
    | comparisonOperator
    | explainMode
    | correlationType
+   | geoIpProperty
    // commands assist keywords
+   | GEOIP
+   | OVERRIDE
+   | ARROW
    | IN
    | SOURCE
    | INDEX