This introduces optional helper function in tvix/tracing for trace
propagation and uses these helper in the `tvix-store`.
The GRPCBlobService, GRPCDirectoryService and GRPCPathInfoService now
accept a generic client, meaning the client can be generated with either
`::new` or `::with_interceptor`.
This was tested and validated by starting a `tvix-store daemon` and
`tvix-store import`.
Change-Id: I4b194483bf09266820104b4b56e4a135dca2b77a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11863
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
639a00e2ab