postmaster: Reduce verbosity of environment dump debug message

postmaster: Reduce verbosity of environment dump debug message

Emitting each variable separately is unnecessarily verbose / hard to skim
over. Emit the whole thing in one ereport() to address that.

Also remove program name and function reference from the message. The former
doesn't seem particularly helpful and the latter is provided by the elog.c
infrastructure these days.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/leouteo5ozcrux3fepuhtbp6c56tbfd4naxeokidbx7m75cabz@hhw6g4urlowt