feat!: send ERPNext requests as native JSON (use_json_request_body)

Opt ERPNext into native application/json request bodies (frappe#40237).
Non-GET requests to erpnext.* endpoints now send args as a JSON body
instead of form-encoded, per-key JSON-stringified values. Safe after the
preceding commits hardened every whitelisted endpoint with frappe.parse_json.

erpnext/hooks.py

@@ -712,6 +712,10 @@ default_log_clearing_doctypes = {
 
 export_python_type_annotations = True
 
+# Send non-GET requests for ERPNext's endpoints as native `application/json`
+# bodies instead of form-encoded, per-key JSON-stringified values.
+use_json_request_body = True
+
 fields_for_group_similar_items = ["qty", "amount"]
 
 # Translation