Import gojail pkg into runj repo

[gizahNL]

Issue number: #12

Description of changes: This imports the gojail package originally developed at https://github.com/gizahNL/gojail into the runj repository to allow for a simpler co-evolution. Also it modifies the start, delete and entrypoint commands to use the gojail library instead of relying on the jail and jexec os utilities.

Testing done: Jail creation & deletion are working.

Terms of contribution:

By submitting this pull request, I agree that this contribution is licensed under the terms found in the LICENSE file.

[samuelkarp]

Thanks again for opening this and showing me how to properly invoke the jail syscalls. I've adapted some of the work you did here into https://github.com/samuelkarp/runj/commit/398df9a0deea637af3062df1cf846a8d5d11bd49 and pushed that; as a result, this PR now has merge conflicts. I took the approach that I had described (eliminating the map[string]interface{} maps), but I've only implemented the minimum necessary to migrate runj-entrypoint over to the syscall-based approach. The new integration tests continue to pass and I've run this through a basic manual test with containerd and it seems to be working properly there too.

I'm still not sure of some of the things that I had asked you (including the "errmsg" iovec) so I didn't integrate that into my commit.

You'll note that I credited you in the commit with Co-authored-by. I'd love help understanding and implementing the rest if you have the time for it.