Configure tree shaking of TS files in the build so that only imported properties get transpiled rather than entire packages.

Example of importing date-fns:
https://github.com/statisticsnorway/mimir/blob/master/src/main/resources/lib/ssb/utils/dateUtils.ts#L1

This currently transpiles the entire date-fns package instead of only enGB, nb, nn.

Another issue is that internal imports don't seem to be replaced by require.
This local import (./dateUtils) is currently inlined on transpilation in all its entirety:
https://github.com/statisticsnorway/mimir/blob/master/src/main/resources/lib/ssb/utils/articleUtils.ts#L9