PR30316: debuginfod wal checkpointing

PR30316: debuginfod wal checkpointing

Add a "--scan-checkpoint=NUM" option to debuginfod to control forced
synchronization & sqlite -wal checkpointing for the multithreaded
scanning process.  In absence of this, a server that's busy with other
read & write operations can accumulate potentially large SQLITE WAL
temporary files.  This option causes the server to take intermittent
quiescent breaks during scanning, during which the -wal file can be
processed and truncated.

Signed-off-by: Frank Ch. Eigler <fche@redhat.com>