Support Poisson distributed requests for benchmark

[CharleneHu-42]

Description

Support the generation of requests that follows poisson distribution in benchmark.
User can set requests to poisson distribution and configure average request arrival rate in benchmark.yaml as:

  load_shape:              # Tenant concurrency pattern
    name: poisson
...
      poisson:                 # Poisson load shape specific parameters, activate only if load_shape is poisson
        arrival-rate: 1.0        # Request arrival rate

Issues

N/A

Type of change

• New feature (non-breaking change which adds new functionality)

Dependencies

None

Tests

Local tests

[Zhenzhong1]

Including some performance data or conclusions for different kinds of request distribution in this PR would be great if available.