Feature Request: New Sideloading Sources

I'm sure there's already internal issues/plans for additional sideloading sources, but I didn't see any public issues yet.

Here are some additional sideloading sources that might be useful:

* Script/exec source (execute a script, return YAML data)
* HTTP/S source (e.g. issue an HTTPS ``GET``, return YAML data)
* Redis source (e.g. ``HGETALL`` a hash and load data)

Related issues #722, #981

No files, tests, or entry points are named. Start by reviewing related issues #722 and #981, then clarify the expected interfaces and behavior for script/exec, HTTP/S, and Redis sources. Done would mean an agreed implementation scope for loading YAML or Redis hash data from the proposed sources.

Written by the indexing model from the issue text.