To add arbitrarily formatted string of {value}.

Currently, there is no easy way to add formatted value, i.e 1000.123 -> $1,000.12. {f_value} basically accepts any arbitrary values for now. Further consideration can be put in place to make use of Numeral-js (https://github.com/adamwdraper/Numeral-js).

The concept is similar to what Google Charts API has on displaying a formatted value, i.e. ArrowFormat example in https://developers.google.com/chart/interactive/docs/reference#formatters