refactor: configurable exchange gain or loss posting date

[ruthra-kumar]

In Payment Reconciliation, the pop-up for settings difference amount will have posting date field as well.

[codecov]

Codecov Report

Merging #37630 (514d543) into develop (38ca164) will increase coverage by 0.47%.
Report is 133 commits behind head on develop.
The diff coverage is 77.27%.

@@             Coverage Diff             @@
##           develop   #37630      +/-   ##
===========================================
+ Coverage    66.86%   67.34%   +0.47%     
===========================================
  Files          791      757      -34     
  Lines        62519    60098    -2421     
===========================================
- Hits         41805    40472    -1333     
+ Misses       20714    19626    -1088     

Files	Coverage Δ
...account_closing_balance/account_closing_balance.py	97.91% <100.00%> (+4.29%)	⬆️
...xt/accounts/doctype/payment_entry/payment_entry.py	83.77% <100.00%> (+0.08%)	⬆️
...e/payment_reconciliation/payment_reconciliation.py	93.79% <100.00%> (+0.02%)	⬆️
...xt/accounts/doctype/sales_invoice/sales_invoice.py	83.88% <100.00%> (-0.08%)	⬇️
...nts/doctype/subscription_plan/subscription_plan.py	40.47% <ø> (ø)
erpnext/accounts/doctype/tax_rule/tax_rule.py	93.10% <100.00%> (+1.36%)	⬆️
.../report/accounts_receivable/accounts_receivable.py	90.56% <100.00%> (ø)
...omparison/general_and_payment_ledger_comparison.py	100.00% <100.00%> (ø)
erpnext/accounts/utils.py	73.16% <100.00%> (-1.60%)	⬇️
erpnext/controllers/selling_controller.py	79.88% <100.00%> (-0.88%)	⬇️
... and 37 more

... and 18 files with indirect coverage changes