Message registries continuation

[Matt Spinler <mspinler@linux.ibm.com>]

Hi James,

Picking up the discussion again from 
https://lists.ozlabs.org/pipermail/openbmc/2020-February/020620.html
about reading  in message registries...

When this was left off, I believe we were leaning toward being able to 
copy message registry JSON files
into some target directory on the BMC during the build where bmcweb 
would load them on startup
and leave them in their JSON objects, and they would be pulled from 
there when LogService requests
were made.

This was to be able to support multiple languages, and in general just 
to support other registries besides
the existing OpenBMC one that is hardcoded in a header file.  (We're 
going to have an IBM registry we
use together with our D-Bus logs based LogService.)

An open issue we still had was if these registries had to be validated, 
or if that was left to whoever
made them.  A stake in the ground could be that we leave the OpenBMC 
registry as it is in a header
file, which negates validation, or put it in JSON too and validate just 
that one during the build.
Or if there are any other ideas here...

As far as the directory used, I think that /usr/share/bmcweb/ would be 
appropriate, or maybe
/usr/share/bmcweb/registries/ if either of those are OK with you.

Also, it may be overkill to need to  read in the same registry for every 
language, as there could
be dozens and realistically they will never all be used on a single 
system, but if the desire is only
to load them at startup before the current language is known I don't 
really see a way around it.

Thanks!
Matt