Add allow_partial parameter to the "coins to spend" query

.changes/added/2912.md

@@ -0,0 +1 @@
+Add the `allow_partial` parameter to the `coinsToSpend` query. The default value of this parameters is `false` to preserve the old behavior. If set to `true`, the query returns available coins instead of failing when the requested amount is unavailable.

crates/client/assets/schema.sdl

@@ -1281,6 +1281,10 @@ input SpendQueryElementInput {
 	The maximum number of currencies for selection.
 	"""
 	max: U16
+	"""
+	If true, returns available coins instead of failing when the requested amount is unavailable.
+	"""
+	allowPartial: Boolean
 }
 
 type SqueezedOutStatus {