EventsSDK: Revise Authorization in AnalyticsConfig

[ejaffee01]

Previously we had to fields in AnalyticsConfig that we're optional, key and bearer, where we throw an error if none or both are set. This change updates the interface so it is more clear that only one is required. There is now authorizationType which is either a string apiKey or Bearer and authorization which is the token itself. We need authorizationType so we can append the proper prefix of KEY or Bearer to the final authorization property to avoid passing this work onto the user. This also updates necessary test files to reflect this change, and removes logic for ensuring that only one of key or bearer is set.

J=FUS-6201
R=abenno, mtian, mkilpatrick
TEST=auto