[org-cite] add convention for direct commands, process for adding mappings to export processor(s)?

[Bruce D'Arcus]

The current list of styles and variants included in the oc export
processors was a first step, with a goal to provide a solid starting
point, and citations that are more-or-less portable across the
backends.

But that raises an obvious question: what next?

I'd like, for example, to suggest adding "noauthor/bare" -> "cite*" to
oc-biblatex.

I also think we should add a way for users to use a direct command for
natbib and biblatex.

As I've looked into some of what I'd call corner cases, consistency
breaks down a bit, so it may not be advisable to add explicit support
for certain options, since they won't work across different backends
anyway.

Perhaps some prefix for a style that signals to pass on directly for a
specific export processor; like [cite/blx+footcite ...].

In that case, the oc-biblatex processor would pass that command on as
is, but other processors would ignore it, and use the default instead.

The documentation would just need to emphasize use of such commands
would necessarily tie those citations to the specific export backend.

And if we were to add this, we'd still need to answer my first
question: when and how to add specific style/variant mappings to the
oc processors.

Thoughts?

Bruce