Meta signature collection in relay scenario

[roman-khimov]

Expected Behavior

When a node is just a relayer (it doesn't store an object) it should still collect/push meta signatures since it's the one responsible for replication.

Current Behavior

Only "local node" handles signatures.

Possible Solution

Fix it.

Context

#2878, #3029.

Your Environment

• Version used: master
• Server setup and configuration:
• Operating System and version (uname -a):

[carpawell]

As we know, "relay" works only in external slicing/full object complete cases and we have not experienced such problems for years and only after we saw our own objects from neo-go team we failed for the first time. It is currently impossible to collect any signatures due to the API that is used in relay (PUT, not REPLICATE), also relay uses all the nodes and takes part in placement logic. I suggest paraphrasing the issue to "fix the relay process" to make it more natural and changing its priority. Not expect problems from our clients for now. @roman-khimov