Describe the bug
When trying to update metrics_generator.processors through the user-configurable overrides, when the array contains the processor span-metrics-size, the request is rejected with metrics_generator.processor "span-metrics-size" is not a known processor, valid values: [service-graphs span-metrics local-blocks].

To Reproduce
Steps to reproduce the behavior:

1. Start Tempo (SHA or version)
2. Update metrics_generator.processors through the user-configurable overrides

Expected behavior
span-metrics-size is a valid subprocessor of the span-metrics processor and should be accepted.

Environment:
N/A

Additional Context