gRPC: Allow retries of up to MAX_MSG_SIZE (#347)

## Problem

gRPC has a built-in retry mechanism[1] which we configure to
automatically retry on status UNAVAILABLE messages from Pinecone.

However, it has been observed that VectorService/Upsert method is _not_
being retried automatically and causes an exception to be thrown to the
application:

    Traceback (most recent call last):
File ".venv/lib/python3.11/site-packages/pinecone/grpc/base.py", line
150, in wrapped
	return func(
	       ^^^^^
File ".venv/lib64/python3.11/site-packages/grpc/_channel.py", line 1181,
in __call__
	return _end_unary_response_blocking(state, call, False, None)
	       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File ".venv/lib64/python3.11/site-packages/grpc/_channel.py", line 1006,
in _end_unary_response_blocking
	raise _InactiveRpcError(state)  # pytype: disable=not-instantiable
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
grpc._channel._InactiveRpcError: <_InactiveRpcError of RPC that
terminated with:
	    status = StatusCode.UNAVAILABLE
	    details = "unavailable"
debug_error_string = "UNKNOWN:Error received from peer
ipv4:34.223.120.220:443
{created_time:"2024-05-10T11:54:43.047741403+00:00", grpc_status:14,
grpc_message:"unavailable"}"

Enabling gRPC's tracing[2] by setting env vars 'GRPC_VERBOSITY=debug
GRPC_TRACE=all' (warning - this is _very_ verbose!) highlighted that
when we do get an StatusCode.UNAVAILABLE, retry is not considered as the
request is too large ("committing" in this context means it effectively
disables retry attempts):

0514 14:00:43.870499051 4093173 retry_filter_legacy_call_data.cc:1855]
chand=0x7ff708006080 calld=0x56377b0b11e0: exceeded retry buffer size,
committing

As per gRPC's options[3], the max buffer size is controlled via:

    /** Per-RPC retry buffer size, in bytes. Default is 256 KiB. */
#define GRPC_ARG_PER_RPC_RETRY_BUFFER_SIZE
"grpc.per_rpc_retry_buffer_size"

Given Upsert messages are frequently larger than 256KiB (it is common to
batch up to the 2 MB limit), we will fail to retry any batches larger
than 256kB.

## Solution

Address this by changing the retry buffer size to the same size as the
maximum message we support (currently 128MB, more than sufficient to
retry any UpsertRequest).

[1]: https://grpc.io/docs/guides/retry/
[2]:
https://github.com/grpc/grpc/blob/master/doc/environment_variables.md
[3]:
https://github.com/grpc/grpc/blob/befeeba0f57c6ed3608935d8317fd26289e7e080/include/grpc/impl/channel_arg_names.h#L321

## Type of Change

- [x] Bug fix (non-breaking change which fixes an issue)

## Test Plan

No existing test infra to automate testing of this (no way to do error
injection); manually verified that previously seen (intermittent)
UNAVAILABLE responses are correctly retried.

pinecone/grpc/base.py

@@ -98,6 +98,7 @@ def _gen_channel(self, options=None):
             "grpc.max_receive_message_length": MAX_MSG_SIZE,
             "grpc.service_config": self.method_config,
             "grpc.enable_retries": True,
+            "grpc.per_rpc_retry_buffer_size": MAX_MSG_SIZE,
         }
         if self.grpc_client_config.secure:
             default_options["grpc.ssl_target_name_override"] = target.split(":")[0]