use Info level for excluded databases log message

[keegancsmith]

This is the only log message which didn't specify a level in the postgres_exporter. I am unsure if this log message should be info or debug, but leaning towards the more important since previously it would just always log.

The way I validated this was the only non-leveled logger was via grep. Both of these only returned this callsite previously:

git grep 'logger\.Log'
git grep '\.Log(' | grep -v level

[keegancsmith]

I saw that the last PR that wasn't made by a bot did a ping on some people to get it reviewed. So hope you don't mind me pinging ya for this tiny change @SuperQ @sysadmind