Updates to staff payment validation error in Nuxt Layers

**Update staff payment validation and move into the business layer**

Design Ticket #30278

Add validation errors for the following input fields on the staff payment component
- Routing Slip Number: Routing Slip Number must be 9 digits
- Display if user enters anything that is not a digit; Triggers immediately; 
Stop displaying as soon as user removes the non-digit character
- Display if user enters more or less than 9 characters; Triggers when user leaves the field (but only if field is not empty)
; Stop Displaying as soon as input value becomes exactly 9 numeric digits
- BC Online Account Number: BC Online Account Number must be 6 digits
- Display if user enters anything that is not a digit; Triggers immediately; Stop displaying as soon as user removes the non-digit character
- Display if user enters more or less than 6 characters; Triggers when user leaves the field (but only if field is not empty)
 Stop Displaying as soon as input value becomes exactly 6 numeric digits
- DAT Number: DAT Number must be in standard format (eg, C1234567)
- Display if user enters anything other than standard format 
(starts with C and has 7 numbers afterwards. No spaces allowed); Triggers when user leaves the field (but only if field is not empty); Stop Displaying as soon as it is entered in standard format