add "--force" flag in add-node command

[thedebugger]

Is this a BUG REPORT or FEATURE REQUEST?: feature request

What happened: There is no "--force" option in the add-node command https://github.com/apprenda/kismatic/blob/036c1073599b1a3eb101349ddb77afc336db8cff/docs/kismatic-cli/kismatic_install_add-node.md

What you expected to happen: Could we add it so that we can add a node even it is present in kismatic.yml? We use kismatic installer. And, when an existing node fails, we destroy and recreate it. But, when we try to add it back, kismatic won't let us because it has reference in kismatic.yml file. So it would be nice to add "--force" for this use case.

How to reproduce it (as minimally and precisely as possible): N/A

Anything else we need to know?: Let me know if you have any questions

Environment: N/A