dynamic reconfiguration of smeshers used in the node

[dshulyak]

for static configuration see #5089
for supported interface see #5085

in addition to loading smeshers from disk we can implement trusted API to register smeshers. such API will have to:

• save a key to the same or different location
• register key to all protocols that support it (implement Register method)

to implement this we can add grpc API. note that this will be trusted API, if people will want to expose it and do pool-like software authentication is on them.