Add a simple finagle/grpc benchmark

[xerial]

Added a simple benchmark to see the performance of gRPC compared to Finagle:

> benchmark/pack

$ ./airframe-benchmark/target/pack/bin/airframe-benchmark bench -mt 5s http
Benchmark              Mode  Cnt     Score      Error  Units
FinagleBenchmark.rpc  thrpt   10  3780.651 ± 2274.439  ops/s
GrpcBenchmark.rpc     thrpt   10  6665.655 ± 2034.274  ops/s

Generally, gRPC seems 1.5 ~ 2x faster than Finagle.

Updates

Added async RPC call results as well:

Benchmark                   Mode  Cnt      Score      Error  Units
FinagleBenchmark.rpcAsync  thrpt   10  12540.307 ± 3885.182  ops/s
FinagleBenchmark.rpcSync   thrpt   10   4378.924 ± 1238.384  ops/s
GrpcBenchmark.rpcAsync     thrpt   10  35829.839 ± 3067.464  ops/s
GrpcBenchmark.rpcSync      thrpt   10   6355.409 ± 1586.169  ops/s

gRPC is super fast: 35,829 rpc/sec: 5x faster than sync client and 3x faster than finagle-async client!

[codecov]

Codecov Report

Merging #1247 into master will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1247   +/-   ##
=======================================
  Coverage   83.30%   83.31%           
=======================================
  Files         296      296           
  Lines       11414    11415    +1     
  Branches      715      725   +10     
=======================================
+ Hits         9509     9510    +1     
  Misses       1905     1905           

Impacted Files	Coverage Δ
...shared/src/main/scala/wvlet/log/io/StopWatch.scala	80.20% <0.00%> (+0.20%)	⬆️

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