Add morph client metrics

[carpawell]

It could count switches, call durations, etc.

[carpawell]

In fact, i would create an epic about metrics (devs for devs): i would be happy to see Replicator/Policer, TreeService, disk metrics by a shard (blobovnicza number, small vs big objects, writecache's memory/objects usage, etc), etc.

[fyrchik]

Let's leave this task for morph client and create new issues for other components (with concrete list of what we want)
For morph I suggest:

1. Endpoint switches count
2. Received notifications count by type (and endpoint?)
3. Last block received
4. For each contract, executed method count (duration?)