Allow fee payment with insufficient asset

[jak-pan]

Insufficient asset will be only possible to use for payment when they have XYK pool with DOT or HDX.

Add special function for XYK to buy fee -> Same XYK buy math but the destination is treasury. ( saving 1 transfer and allowing to skip the triggers cc @enthusiastmartin )

When user selects such asset for fee payment, we need to have pool with DOT or HDX, buy the fee in the pool and directly transfer to treasury instead of sending insufficient asset.

(Can we do this with XCM?)