Fix antlr4 parser issues

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

Author: LantaoJin

ppl/src/main/antlr/OpenSearchPPLLexer.g4

@@ -36,7 +36,6 @@ AD:                                 'AD';
 ML:                                 'ML';
 FILLNULL:                           'FILLNULL';
 TRENDLINE:                          'TRENDLINE';
-PATTERN_METHOD:                     'PATTERN_METHOD';
 SIMPLE_PATTERN:                     'SIMPLE_PATTERN';
 BRAIN:                              'BRAIN';
 VARIABLE_COUNT_THRESHOLD:           'VARIABLE_COUNT_THRESHOLD';
@@ -417,7 +416,7 @@ INTEGER_LITERAL:                    DEC_DIGIT+;
 DECIMAL_LITERAL:                    (DEC_DIGIT+)? '.' DEC_DIGIT+;
 
 fragment DATE_SUFFIX:               ([\-.][*0-9]+)+;
-fragment CLUSTER_PREFIX_LITERAL:    [*A-Z]+?[*A-Z_\-0-9]* COLON;
+fragment CLUSTER_PREFIX_LITERAL:    [*a-zA-Z]+?[*a-zA-Z_\-0-9]* COLON;
 ID_DATE_SUFFIX:                     CLUSTER_PREFIX_LITERAL? ID_LITERAL DATE_SUFFIX;
 DQUOTA_STRING:                      '"' ( '\\'. | '""' | ~('"'| '\\') )* '"';
 SQUOTA_STRING:                      '\'' ('\\'. | '\'\'' | ~('\'' | '\\'))* '\'';
@@ -426,7 +425,7 @@ fragment DEC_DIGIT:                 [0-9];
 
 // Identifiers cannot start with a single '_' since this an OpenSearch reserved
 // metadata field.  Two underscores (or more) is acceptable, such as '__field'.
-fragment ID_LITERAL:                ([@*A-Z_])+?[*A-Z_\-0-9]*;
+fragment ID_LITERAL:                ([@*a-zA-Z_])+?[*a-zA-Z_\-0-9]*;
 
 
 ERROR_RECOGNITION:                  .    -> channel(ERRORCHANNEL);

ppl/src/main/antlr/OpenSearchPPLParser.g4

@@ -983,6 +983,7 @@ keywordsCanBeId
    | multiFieldRelevanceFunctionName
    | commandName
    | comparisonOperator
+   | patternMethod
    // commands assist keywords
    | IN
    | BETWEEN
@@ -994,6 +995,9 @@ keywordsCanBeId
    | FROM
    | PATTERN
    | NEW_FIELD
+   | VARIABLE_COUNT_THRESHOLD
+   | FREQUENCY_THRESHOLD_PERCENTAGE
+   | WITH
    | REGEX
    | PUNCT
    | USING
@@ -1048,10 +1052,6 @@ keywordsCanBeId
    | LAST
    | LIST
    | VALUES
-   | EARLIEST
-   | EARLIEST_TIME
-   | LATEST
-   | LATEST_TIME
    | PER_DAY
    | PER_HOUR
    | PER_MINUTE
@@ -1069,4 +1069,6 @@ keywordsCanBeId
    | FULL
    | SEMI
    | ANTI
+   | LEFT_HINT
+   | RIGHT_HINT
    ;