Bug Fix: updating ps_stat_statements query to have distinct records

[Good villain gv]

Hi,

I had proposed a fix for the issue GIT ISSUE REPORTED where metrics exporter errors out and stop collecting metrics upon dupliciate query id.

Pull request submitted for the same. CLICK HERE TO PR

Test builds are completed with no error. awaiting for review and merge. can you please check and merge this branch. as this could help community users of prometheus.

Thanks & Regards,

Viggu