pgsql: Add some checkpoint/restartpoint status to ps display

Add some checkpoint/restartpoint status to ps display

This is done for end-of-recovery and shutdown checkpoints/restartpoints
(end-of-recovery restartpoints don't exist) rather than all types of
checkpoints, in cases where it may not be possible to rely on
pg_stat_activity to get a status from the startup or checkpointer
processes.

For example, at the end of a crash recovery, this is useful to know if a
checkpoint is running in the startup process, while previously the ps
display may only show some information about "recovering" something,
that can be confusing while a checkpoint runs.

Author: Justin Pryzby
Reviewed-by: Nathan Bossart, Kirk Jamison, Fujii Masao, Michael Paquier
Discussion: https://postgr.es/m/20200818225238.GP17022@telsasoft.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/df9274adf3096feafbbde2562311c8ab80405267

Modified Files
--------------
src/backend/access/transam/xlog.c | 45 +++++++++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)