Conform zipkin traceId, spanId, parentId specs

[praxist]

Using v1 API defined in https://github.com/openzipkin/zipkin-api/blob/7692ca7be4dc3be9225db550d60c4d30e6e9ec59/zipkin-api.yaml

traceId to 32 character lowercase hex string spanId to 16 character lowercase hex string parentId to be absent for root span

Currently required changes to prove out a grafana-agent + tempo tracing architecture.

[fishy]

This needs to be opt-in and default to false, as the older version of baseplate.py/go library will reject hex ids.

We already implemented the opt-in in .go, see the comment there: https://pkg.go.dev/github.com/reddit/baseplate.go/tracing#TracerConfig.UseUUID