[FEATURE] Adjustable decimals for view helper format.currency

Adds an extra attribute to set number of decimal points.

Releases: 6.1
Resolves: #45673
Fluid Package Issue: #45923
Change-Id: I687ced95a0b7a081a669dc8883d39b19542d691c
Reviewed-on: https://review.typo3.org/18528
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring