Adapt the Bootstrap feature to the CLI

[nluaces]

New commands:

• skupper system ~start~ setup
• skupper system reload (equivalent to skupper system ~start~ setup -f)
• skupper system stop
• skupper system teardown ~(replaces remove.sh script)~

The bootstrap logic was moved to pkg/nonkube/bootstrap. I'm open to move those files to new locations or any kind of renaming that makes more sense.

Other updates:

• Removed: ~remove.sh and~ bootstrap.go
• Updated README and bootstrap.sh
• Updated Makefile and config.yaml to replace bootstrap image by ~skupper-~ cli image