Set money aside as awaiting payment for Invoices that are 'Approved'

Note: This was split from UXPROD-2295 so that it could be worked on independently.

Overview: If an invoice is created with no reference to an order line or no reference to any encumbrances through order lines. There is no money committed for the value of the invoice until it is 'Paid'.

Note: RM SIG discussion revealed that we must commit money on approval at very least so awaiting payment values are accurate. Also, Transactions must have links to invoice(s) that contribute to awaiting payment value and this will be created as separate feature. Finally, for some institutions waiting until "Approved" to commit is later than desired so a separate feature will be created to capture work allowing a pending invoice state so Open invoice values can be committed.

Use cases:
User approves invoice and does not realize that there is not enough money left in their chosen funds to cover the invoice until trying to pay the invoice
Administrator is reviewing the current state of finances and can not see how much money they have currently committed to spend because some of the approved invoice amounts are not counted against available budget values as awaiting payment

Requirements

• Users need the money committed as soon as the invoice(s) are approved
• Transaction representing this should be identified as 'Awaiting payment'
• Display amount 'Awaiting payment' separate from encumbered in transaction list.
• Once 'Payment' is created the "Pending payment" transaction will no longer display in transaction list

Proposed approach:

• Create 'Pending payment' encumbrances with 0 initial encumbered value to put money aside for payment when the invoice is approved. Conduct all necessary checks for available money. (Note this check should be against the Allowable Expenditure NOT Allowable Encumbrance)
• Pending payment is displayed as the type of transaction when source is "Invoice".
• When Payment is created the "Pending payment" encumbrance is 'release' transaction with initial encumbrance of 0 that are release no longer display in transaction list

Questions for dev team:

• Should we create a new transaction type or use Encumbrance transaction type and adjust label? Yes transaction type "Pending payment" will be used