Provide porcelain flag in eval for mounting the current directory

[frankfarzan]

Often times, when running functions that require access to the host filesystem, you want to operate on package hierarchy in the current working directory. Consider providing a short-hand for doing:

type=bind,src="$(pwd)",dst=/cwd,rw=true

e.g.

--mount-current or something like that.

Need to consider a convention for the default directory in the container.

https://kpt.dev/book/04-using-functions/02-imperative-function-execution?id=mounting-directories

[droot]

Yes, this is definitely needed.