Transmit response signature failures as gRPC status error instead of panic

[cthulhu-rider]

response signature problem cannot be transmitted as valid NeoFS API response. Currently, node just panics:

neofs-node/pkg/services/util/sign.go

Lines 170 to 174 in b9fbe92

	if err := signature.SignServiceMessage(signer, r2); err != nil {
	// We can't pass this error as NeoFS status code since response will be unsigned.
	// Isn't expected in practice, so panic is ok here.
	panic(err)
	}

i propose to replace panic with gRPC status error:

• client will be able to realize whats goin on
• no panic in realistic, although not much expected, case

Context

#3084

[cthulhu-rider]

Object service also pushes exec errors into metrics. We should definitely submit the original error, not just signing one. Do we need to also push sign error? Well, it can be useful overall. Joining can also be considered

we can also consider switching to degraded state when a node loses the ability to sign responses, but this is a separete issue