[feature request] add an option to make a framework's spans be on it's own trace tree

[mikeldking]

Right now it can be a pretty expensive query to figure out "root" spans. We should consider letting frameworks use their own traces so that they can be isolated more cleanly

'''
from opentelemetry import trace
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import SimpleSpanProcessor, ConsoleSpanExporter
from opentelemetry.trace import set_span_in_context

Set up the tracer provider and exporter

trace.set_tracer_provider(TracerProvider())
tracer = trace.get_tracer(name)
trace.get_tracer_provider().add_span_processor(
SimpleSpanProcessor(ConsoleSpanExporter())
)

Start a new root span (i.e., with a new trace ID)

with tracer.start_as_current_span("new-trace-root", context=None) as span:
print(f"Started new trace with trace_id: {format(span.get_span_con
'''