aggregate externals

[crherman7]

Is your feature request related to a problem? Please describe.
Module resolver babel plugin i.e. ts aliases will be treated as external dependencies. We need users right now to add those to the .rechunkrc.json which is not ideal.

Describe the solution you'd like
Automatically aggregate all of these based on tsconfig.json file and traverse imports to match and expand array of those externals.

Describe alternatives you've considered
Leave as is.