Add saf convert:hdf2splunk and saf convert:splunk2hdf

[ejaronne]

based on https://github.com/mitre/hdf-json-to-splunk and heimdall's Splunk load capability.

[Amndeep7]

@camdenmoors in order to get it out for integration with other services, I'm merging the hdf2splunk pr which seemed like it was mostly in an alright state besides some minor build issues when using yarn build/pack that I resolved, which resulted in hdf-converters getting all the way up to 2.6.13 - please review the changes I made to make sure you're caught up on changes that are relevant for you.

anyways, things that i see left to do are:

• [ ] test? we somehow have tests running on heimdall so presumably we should be able to get them hooked up here
• [x] documentation on the readme. this one is partially intentional to avoid attracting too much attention to the new functionality since it's still in an intermediary state.
• [ ] 'insecure' flag - similar to hdf2asff, we might need to add options and stuff to handle self-signed-cert/tls issues: https://stackoverflow.com/questions/10888610/ignore-invalid-self-signed-ssl-certificate-in-node-js-with-https-request