Add OpenTelemetry support

[pquentin]

Based on the OpenTelemetry work made in the client itself.

Here are the pull requests to backport:

• Pass endpoint_id and path_parts to transport elasticsearch-py#2457
• Add OpenTelemetry end-to-end test elasticsearch-py#2466
• Make test_otel more robust to elastic-transport changes elasticsearch-py#2470
• Run OpenTelemetry integration test separately elasticsearch-py#2479
• Type endpoint_id and path_parts as Optional elasticsearch-py#2482
• Move OpenTelemetry context manager to main client elasticsearch-py#2490
• Document and enable OpenTelemetry instrumentation elasticsearch-py#2491

Done with those pull requests:

• Pass endpoint_id and path_parts to BaseClient #69
• Add OpenTelemetry support #70