[Feature Request] Make config.ts async to allow for things like kms decrypt calls for ENV variables

[medhost-jshaver]

Is your feature request related to a problem? Please describe.
Currently cannot make async calls from config.ts. I would like to pass kms encrypted ENV variables for the client_id/secret attributes of introspectionOptions and be able to call kms.decrypt() within config.ts/authZConfig.ts (for smart).

Describe the solution you'd like
I would be nice to have config.ts and authZConfig.ts (for smart) handle async methods.

Describe alternatives you've considered
We could make the kms decrypt call from the authz-smart package right before using the client_id/secret values for basic credentials, but this would be called for every request and seems like unnecessary overhead.

[rsmayda]

Hey Josh,

Lets set up some time to discuss more!

[carvantes]

This was added on #464