Consider new packages for metrics and logging, and tracing

[tsloughter]

As we get closer to needing to decide on moving metrics, and then logging, into the main SDK package I thought we should consider breaking up the applications the same as some other languages do the packaging.

This would look something like:

opentelemetry_api_tracing
opentelemetry_sdk_tracing
opentelemetry_api_metrics
opentelemetry_sdk_metrics

(Not sure about logging yet because I don't think it has an API).

And we would publish packages opentelemtry_api that only includes opentelemetry_api_tracing and a package opentelemetry that only includes opentelemetry_sdk_tracing. Eventually those packages would be sunset.

[tsloughter]

Note that there may be events and profiling Signals, and thus packages, eventually as well.

[ferd]

I guess this will make sense most and be worth it once/if we have to pull in dependencies for these, which would possibly clash with people using similar dependencies in other applications (possibly related to metrics already). Otherwise the cost of a few modules wouldn't worry me either.

Since they all need to call to the same underlying libraries, do you think this better scopes compatibility issues as well? I guess if so it could help, and that the current 'experimental' subset of libs and modules did that namespacing at a lower level than the library level.