This is an opt-in mode, that will make data in the workspace
read-only, thus protecting cache from corruption when hardlinks or
symlinks are used. User can use `dvc unprotect file` command, to
replace read-only link to cache with an editable copy. We can use
this for now to decide if we want to go with a `unified workflow`
in the future or if we want to set unprotected `reflink,copy`
by default.
Fixes#799
Signed-off-by: Ruslan Kuprieiev <[email protected]>