[BUG] StatusCode.UNAVAILABLE grpc response when reaching armeria connection limit

Describe the bug

The OTel trace source is configured with a connection limit (max_connection_count) which defaults to 500.

In case this limit is reached Data Prepper logs sth. like:

[armeria-boss-http-*:21890] WARN  com.linecorp.armeria.server.ConnectionLimitingHandler - Dropped 10 connection(s) to limit the number of open connections to 500 

and returns a StatusCode.UNKNOWN:

<_InactiveRpcError of RPC that terminated with:
	status = StatusCode.UNKNOWN
	details = "Received http2 header with status: 500"
	debug_error_string = "UNKNOWN:Error received from peer  {grpc_status:2, grpc_message:"Received http2 header with status: 500"}"

This status code is not classified as retryable failure.

Since clients are dropping the connection in this case, I am wondering if Data Prepper should respond with e.g. StatusCode.UNAVAILABLE instead so that this could be retried within the OTel client.

However, if a client consistently reaches the connection limit, retries could again fail of course.

To Reproduce
Steps to reproduce the behavior:

1. Configure data prepper with the trace analytics setup.
2. Reduce the max_connection_count to a lower number so that this is reproducible with e.g. 2 clients.
3. Start Data Prepper and send Otel traces e.g. via the opentelemetry gen tool and an OTel collector inbetween.
4. Observe the logs on DP and the client side.

Expected behavior

• consider returning a different status code which would allow retries.

Environment (please complete the following information):

• DP 2.11.0

Start in the data-prepper-plugins/otel-trace-source area linked in the issue and trace how connection-limit failures become gRPC responses. Reproduce with max_connection_count reduced to two and two clients, then verify that the response uses a retryable status such as UNAVAILABLE without changing other failures.