Change to using arrow functions (#1603)

* Change to using arrow functions

Co-authored-by: v1b3m <vibenjamin6@gmail.com>
Co-authored-by: Matheus <matheus_benini@hotmail.com>

* Add lint rule

---------

Co-authored-by: v1b3m <vibenjamin6@gmail.com>
Co-authored-by: Matheus <matheus_benini@hotmail.com>
Co-authored-by: Charles Bochet <charles@twenty.com>

front/src/utils/format/number.ts

@@ -1,3 +1 @@
-export function formatNumber(value: number): string {
-  return value.toLocaleString();
-}
+export const formatNumber = (value: number): string => value.toLocaleString();