Allow nesting of background span

[RedX2501]

I was not able to make otel-cli span background nest.

This is a very simple example in my real script the calls happen in a nested fashion.

local_otel_run() {
    local span_function="$1"
    shift
    local cli_sockdir="$(mktemp -d)"
    otel-cli span background --name "$span_function" --verbose --tp-required --sockdir "$cli_sockdir" &
    "$span_function" "$@"
    otel-cli span end --sockdir "$cli_sockdir"
}

main(){
   local_otel_run command1
   local_otel_run command2
   local_otel_run command3
}

local_otel_run main

In the logs in Jaeger the main function does not have spans for command1, 2, and 3 displayed nested they are siblings.