Support uninstallation

[farcaller]

To make kasane into a full-featured manager it needs to support object removal. That could be a trivial extension of layers for use cases when there are dynamically created objects.

Can define a global env named mode:

• apply is the current kasane apply action
• remove would allow to add additional objects to be removed with when: mode == 'remove' (also see Loaders for existing k8s objects #10)
• purge would do the remove plus more (e.g. remove all the relevant CRDs)