Generalise proof query/insert RPC endpoints to support transfer proofs

[ffranr]

Generalise proof query and insert RPC endpoints such that they support transfer proofs. They currently only support issuance proofs.

The RPC endpoints are called QueryProof and InsertProof.

This change will include storing transfer proofs within the multiverse.

Deliverables:

• Delete code reference in this comment Generalise proof query/insert RPC endpoints to support transfer proofs #439 (comment)
• Add test to ensure that a transfer proof can be inserted using RPC endpoint InsertProof and retrieved using RPC endpoint QueryProof. #467

[Roasbeef]

So right now the RPC interface doesn't make a distinction between them. The only area we gate things is here:

taproot-assets/universe/base.go

Lines 199 to 205 in 7077464

	// The outpoint of the final resting place of the asset should match
	// the leaf key
	//
	// TODO(roasbeef): this restrict to issuance
	case assetSnapshot.OutPoint != key.MintingOutpoint:
	return nil, fmt.Errorf("outpoint mismatch: expected %v, got %v",
	key.MintingOutpoint, assetSnapshot.OutPoint)

[ffranr]

I've renamed this issue and changed the description but the actual work won't deviate from what we've planed for this sprint.

[ffranr]

Addressed here: #473