feat: apply customer withholding automatically on new receipts

Tick Apply Tax Withholding Amount on unsaved customer receipts whose
references include a Sales Invoice carrying withholding: in the
get_payment_entry override (Create > Payment), in the
allocate_amount_to_references doc method (Get Outstanding Invoices /
Paid Amount changes, so the tax row updates live) and on first save.
Saved entries keep the user's choice; unticking now removes the row.
Client script recomputes the row when the checkbox or category changes.

default_thai_company/hooks.py

@@ -196,11 +196,11 @@ doc_events = {
 
 # Overriding Methods
 # ------------------------------
-#
-# override_whitelisted_methods = {
-# 	"frappe.desk.doctype.event.event.get_events": "default_thai_company.event.get_events"
-# }
-#
+
+override_whitelisted_methods = {
+	"erpnext.accounts.doctype.payment_entry.payment_entry.get_payment_entry": "default_thai_company.tax_withholding.get_payment_entry",
+}
+
 # each overriding function accepts a `data` argument;
 # generated from the base implementation of the doctype dashboard,
 # along with any modifications made in other Frappe apps