* feat(cmds/add): --to-files option as files cp
* tests(to-files): ensure error handling is covered
this adds bunch of tests that guard UX around importing multiple files
into MFS, and the logic around trailing slash to indicate if the MFS
destination if a directory.
If the destination has a trailing slash, we ensure that the directory
exists and is a dir and not a file. this allows us to support
adding multipl files into MFS dir:
ipfs add file1.txt file2.txt --to-files /some/mfs/dir/
* docs: to-files helptext
Co-authored-by: Antonio Navarro Perez <antnavper@gmail.com>
Co-authored-by: Marcin Rataj <lidel@lidel.org>