go/common/grpc: Client verbose logging and metrics

[ptrus]

• gRPC global logger is now set to oasis logger even if the code using it doesn't initialize any servers, but only uses gRPC clients (and has grpc verbose logging enabled). Before this happened only if a gRPC server was created:
  • this mostly affects test binaries (such as workloads) which do use gRPC client, but don't initialize any servers.
• adds gRPC client logging interceptors
  • only had these for servers
• adds gRPC client instrumentation
  • only had gRPC metrics for servers

[codecov]

Codecov Report

Merging #3121 into master will increase coverage by 0.08%.
The diff coverage is 91.35%.

@@            Coverage Diff             @@
##           master    #3121      +/-   ##
==========================================
+ Coverage   68.56%   68.65%   +0.08%     
==========================================
  Files         375      375              
  Lines       36962    37037      +75     
==========================================
+ Hits        25342    25426      +84     
+ Misses       8390     8376      -14     
- Partials     3230     3235       +5     

Impacted Files	Coverage Δ
go/common/grpc/grpc.go	85.01% <91.25%> (+1.61%)	⬆️
go/oasis-node/cmd/common/grpc/grpc.go	85.41% <100.00%> (+0.31%)	⬆️
go/consensus/tendermint/api/errors.go	86.66% <0.00%> (-13.34%)	⬇️
go/storage/metrics.go	81.52% <0.00%> (-6.53%)	⬇️
go/keymanager/client/client.go	82.64% <0.00%> (-5.79%)	⬇️
...sensus/tendermint/epochtime_mock/epochtime_mock.go	70.63% <0.00%> (-5.56%)	⬇️
go/worker/common/committee/runtime_host.go	65.71% <0.00%> (-4.77%)	⬇️
go/storage/api/root_cache.go	72.41% <0.00%> (-4.60%)	⬇️
go/consensus/tendermint/apps/staking/state/gas.go	77.58% <0.00%> (-3.45%)	⬇️
go/storage/database/database.go	72.26% <0.00%> (-3.37%)	⬇️
... and 29 more

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