Update transition to Approve considering the expense classes "Code"

Purpose:
Requirement from the UX ticket: Each expense class has a code (extension) that compliments the 'Fund code' of any fund it is assigned to

Requirements/Scope:

1. Update creation of voucher lines upon invoice approval

Approach:

• If expenseClassId specified in fundDistribution:
  • retrieve expense classes by id
  • add Code to Fund code (fundCode-expenseClassCode)
• group fundDistribution by externalAccountNumber (consider same fundCode with different expenseClassCode as separate Fund codes)
• create voucher line for each externalAccountNumber or externalAccountNumber-extensionNumber and this pair must be store in voucher line field "ExternalAccountNumber"
• Fund code + expenseClassCode must be stored in voucher line field "fundCode"

Acceptance criteria:

• logic updated
• unit tests updated
• API tests updated