Multi rfq receive itest

[GeorgeTsagk]

Description

Itest for lightninglabs/taproot-assets#1457

We add a new itest that aims to focus on the multi-rfq aspect of custom channels. It uses a new network topology which allows for multiple asset channel peers and has the following topology

	
	            /---[sats]--> Erin --[assets]--\
	           /                                \
	          /                                  \
	 Charlie  -----[sats]-->  Dave  --[assets]---->Fabia
	          \                                  /
	           \                                /
	            \---[sats]--> Yara --[assets]--/
	

The current itest only focuses on the Multi-Rfq feature of AddInvoice on Fabia, but it will be re-used to test the Multi-Rfq feature of SendPayment when that is introduced.

Within the added itest, Fabia creates a bolt11 invoice with multiple hop hints, which represent the multiple RFQ quotes that get encoded as hop hints in the invoice. This is crucial for the payment to succeed, as the payer has to split the payment and reach Fabia via multiple asset channels.

Based on group-key-support branch