[pg_stat_statements] Strip special characters from query

[ussrlongbow]

Same queries from Windows and Linux clients to PostgreSQL may appear as different texts in pg_stat_statements.query having same query ID, because of different line breaks, which blocks proper matching query text to metrics with queryid label in Prometheus.
Example:

# Series from two replicas, one used by Windows client, another by Linux
$ curl -s 'http://prometheus.local:9090/api/v1/series?match[]=pg_stat_statements_query_id%7Bqueryid=%220000000000%22%7D' | jq .data.[].query 
"SELECT\r\n    "Username"\r\nFROM\r\n    \"Users\"\r\nWHERE\r\n        \"UserID\" = $1"
"SELECT\n    "Username"\nFROM\n    \"Users\"\nWHERE\n        \"UserID\" = $1"

This pull request adds option --[no-]collector.stat_statements.strip_special to remove such symbols from query output.

Authors:
@ussrlongbow
@freehck