Add support for gRPC max connection age configuration

[namannandan]

Description

Add support for server side gRPC max connection age configuration

References:

1. Netty gRPC maxConnectionAge
2. Netty gRPC maxConnectionAgeGrace
3. Default gRPC KeepAlive configuration

Fixes #2999

Type of change

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

Feature/Issue validation/testing

• CI
  • https://github.com/pytorch/serve/blob/master/test/pytest/test_gRPC_inference_api.py
  • https://github.com/pytorch/serve/blob/master/test/pytest/test_gRPC_management_apis.py
• Manual test

# gRPC management connection timeout is set to 5 seconds
$ cat custom_config.properties 
grpc_management_max_connection_age_ms=5000
grpc_management_max_connection_age_grace_ms=0

$ torchserve --ncs --start --model-store ./model_store --ts-config ./custom_config.properties

# Note: Model takes longer than 5 seconds to load
$ time python ts_scripts/torchserve_grpc_client.py register densenet161
## Check densenet161.mar in mar_set : set()
## Register marfile: https://torchserve.s3.amazonaws.com/mar_files/densenet161.mar

Failed to register model densenet161.
Socket closed
python ts_scripts/torchserve_grpc_client.py register densenet161  0.13s user 0.06s system 3% cpu 5.629 total

As can be seen from the test above, the gRPC management connection to register model is closed after the configured 5 seconds (max connection age).

[mreso]

LGTM, please view comments and add some comments on what grace means in this context

[slashvar]

Thanks ! This will allow us to use torchserve with gRPC at scale !