Signature response for initial replication

[roman-khimov]

Is your feature request related to a problem? Please describe.

I'm always frustrated when we can't prove the object was accepted by an appropriate number of nodes. After nspcc-dev/neofs-node#2802 we'll be using replication API exclusively for inter-node communication, so we can extend it a bit more.

Describe the solution you'd like

Extend request with an optional "create" flag, add an optional response field for a single signature.

Describe alternatives you've considered

Sending signatures independently notary-style. Adds additional delay and complexity. Here we directly interact with all parties, so an object entry node can collect all the data easily.

[roman-khimov]

It can be generalized to []byte response field.