node: ensure payload serialisation code doesn't panic

[kcsongor]

The VAA payload serialisation functions are called in the admin server during governance VAA injection. Ideally these functions should not panic (and instead propagate error values) so in case of malformed input, the admin server doesn't crash.
Most functions follow this principle, with a couple of exceptions:

wormhole/sdk/vaa/payloads.go

Lines 389 to 391 in 2712dd3

	if module != IbcReceiverModuleStr && module != IbcTranslatorModuleStr {
	panic("module for BodyIbcUpdateChannelChain must be either IbcReceiver or IbcTranslator")
	}

and the functions that call LefPad

wormhole/sdk/vaa/payloads.go

Lines 430 to 436 in 2712dd3

	if length < 0 {
	panic("cannot prepend bytes to a negative length buffer")
	}
	if len(payload) > length {
	panic(fmt.Sprintf("payload longer than %d bytes", length))
	}