this is the first implementation of spk setup command
related to microsoft/bedrock#986

Note:

1. its command decoration json file has a disabled=true property so that the doc generator will skip it.
2. to test this command out, you need to uncomment a liner in index.ts
3. there are common code between spk init and this command; and these common code/functions are moved to lib folder

Next step: create HLD and Manifest Repo