RFC: Add 'taint' field to pg_control.

Hi,

a significant number of times during investigations of bugs I wondered
whether running the cluster with various settings, or various tools
could've caused the issue at hand. Therefore I'd like to propose adding
a 'tainted' field to pg_control, that contains some of the "history" of
the cluster. Individual bits inside that field that I can think of right
now are:
- pg_resetxlog was used non-passively on cluster
- ran with fsync=off
- ran with full_page_writes=off
- pg_upgrade was used

What do others think?

Perhaps we should rename 'tainted' to something less "blame-y" sounding,
but I can't quite think of something more descriptive than
'cluster_history'.

Greetings,

Andres Freund