otlp: Mimir's OTLP endpoint write request size limit should be configured in the same unit as the metrics producers

[replay]

The OTel collector and Alloy allow the user to configure the batch size limit in samples per batch via the setting send_batch_max_size, but since this limit is defined in samples per batch and not in bytes per batch it is difficult to find the right value which guarantees that the write requests don't exceed Mimir's limit which is defined in bytes per batch, especially because the OTel samples can be of variable size in bytes.