[RFE] add new "kernel log buffer" target, or at least a functions to feed qb_log_custom_open with that effect

[jnpkrn]

It would make a tonne of sense if logging clients running on Linux had
a convenient ability to opt-in to log urgent messages also to kmsg,
since it may be at times backed with actual firmware-specific persistent
storage[1,2] that may obviate various disk synchronization issues,
which may othetwise prevent some before-death messages to be made
durable at all.

Alternative approach could be to utilize persistent storage directly
by the client program, e.g. by dumping a blackbox file there, but
e.g., in case of kernel crash, it is not achievable.

[1] brief notes with links:
https://github.com/abrt/abrt/wiki/pstore-oops
[2] https://lwn.net/Articles/434821/

[jnpkrn]

See also a relevant discussion about an initiative to make some details
rendered on the screen in some form in case of panic, which could
hypothetically contain also some recent lines from dmesg:
http://lkml.iu.edu/hypermail/linux/kernel/1903.1/01594.htmlq