Allow logfire.configure() to return multiple separate non-global logfire configurations

[alexmojaki]

I'm thinking something like my_logfire = logfire.configure(..., global=False). With the default global=True then configure will return the default logfire instance. Otherwise it returns a new instance with a new config object, containing a tracer/meter provider that aren't set as the global providers in OTEL.

All the OTEL instrumentation libraries should accept a tracer/meter provider argument where appropriate instead of setting the global providers, so the methods created in #193 should pass providers from the logfire config.