2a1bd7414b
We introduce a WithSpecFromFile option combinator to allow creation simpler creation of OCI specs from a file name. Often used as the first option in a `SpecOpts` slice, it simplifies choosing between a local file and the built-in default. The code in `ctr run` has been updated to use the new option, with out changing the order of operations or functionality present there. Signed-off-by: Stephen Day <stephen.day@getcruise.com>