Global query (SELECT version();) is being executed per datname

[adivinho]

What did you do?
Exporter is run with the discover the databases flag

What did you expect to see?
The query would be run only once for the database postgres

What did you see instead? Under which circumstances?
The query is run for each discovered database

Environment

• System information:
  Linux 4.14.209-160.339.amzn2.x86_64 x86_64

• postgres_exporter version:
  postgres_exporter 0.0.1-rev (built with go1.15.8)

• postgres_exporter flags:

--auto-discover-databases 
--exclude-databases=template0,template1,postgres

• PostgresSQL version:
  12.6.0