Add support for Arithmetic expressions in DataPrepper expression

[kkondaka]

Is your feature request related to a problem? Please describe.
Add support for Arithmetic expressions in DataPrepper expression.
Some discussion is in previous RFC #1005.

Describe the solution you'd like

Suggested grammar for supporting full Arithmetic expressions in DataPrepper expressions

arithmeticExpression
    : arithmeticExpression (PLUS | MINUS) arithmeticTerm
    | arithmeticTerm
    ;

arithmeticTerm
    : arithmeticTerm (MULTIPLY | DIVIDE) arithmeticFactor
    | arithmeticFactor
    ;

arithmeticFactor
    : Function
    | JsonPointer
    | Integer
    | Float
    | LPAREN arithmeticExpression RPAREN
    | SUBTRACT arithmeticFactor
    ;

This allows for +,=,*,/ arithmetic operators and also functions as operands

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Additional context
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[kkondaka]

This issue will be addressed in two phases. First phase will only support Number literals and functions returning integers in the expression with the following grammar

 expression
     : conditionalExpression EOF
     | arithmeticExpression EOF
     | OTHER {System.err.println("unknown char: " + $OTHER.text);}
     ;

arithmeticExpression
    : function
    | jsonPointer
    | Integer
    | Float
    ;

The rest of the functionality (like supporting arithmetic operators +, -, *, / will be added in the second phase