pgsql: postmaster: Update pmState via a wrapper function

postmaster: Update pmState via a wrapper function

This makes logging of state changes easier - state transitions are now logged
at DEBUG1. Without that logging it was surprisingly hard to understand the
current state of the system while debugging.

Reviewed-by: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Reviewed-by: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Reviewed-by: Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com>
Discussion: https://postgr.es/m/kgng5nrvnlv335evmsuvpnh354rw7qyazl73kdysev2cr2v5zu@m3cfzxicm5kp

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7148cbbdc65d68167967e67ed155c7f1635bc8e7

Modified Files
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src/backend/postmaster/postmaster.c | 79 +++++++++++++++++++++++++++----------
1 file changed, 58 insertions(+), 21 deletions(-)