Add an initial seed codeowners (#645)
Add an initial seed codeowners (#645)

* Add an initial seed codeowners

This lists the personnel currently considered responsible for the SDK
code. It intentionally does not list all of the impacted stakeholders,
and makes no attempt to break down any service responsibilities other
than those for flows and timer.

* Changes per review
globus/globus-sdk-python,globus/globus-sdk-python