Tstats command can't parse where parameter

[51-code]

Describe the bug

There is a test case for a query:
| tstats prestats=f append=true count where host=y BY foobar

which results to the error:

line 46:49 mismatched input 'y' expecting {PIPE, WILDCARD, GET_STRING_WILDCARD, GET_STRING_SINGLE_QUOTED, GET_STRING_DOUBLE_QUOTED, GET_STRING_STRING, COMMAND_TSTATS_MODE_BY}

The parsing is therefore stopped when reaching the "y" token. In the parse tree it can be seen that it is actually parsed as a <GET_FIELD_STRING>, which doesn't match the expected tokens.

Expected behavior

Should parse the "y" as a StringType and continue to the by instruction.

How to reproduce

Test the query above.

Screenshots

Software version

6.1.0

Desktop (please complete the following information if relevant):

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Additional context

tstatsSyntaxParseTest in TstatsSyntaxTests.java has been disabled because of this issue in PR #52.