storageproxyd: Add arguments for storage mapping and max file

Background:
* -f = Allows mapping files in the format `-f file:backing_file`.  This
  can be used for mapping secure storage files like `0` and `persist/0`
  to block devices.  Storageproxyd will handle creating the appropriate
  symlinks in the root datapath
* -m = Allows specifying the the max size constraint for file backed storages.
  The constraint is chosen by giving a file, this allows for passing a
  block device for which a max file size can be queried.  File based
  storages will be constrained to that size as well.

Bug: 324989972
Test: File sizes are restricted as specified, and mappings are created
Change-Id: I8ff550afafbd372288daa9e27c4db3451948b25d
Signed-off-by: Donnie Pollitz <donpollitz@google.com>