Add pgbouncer input plugin (#3918)

plugins/inputs/postgresql_extensible/postgresql_extensible.go

@@ -283,6 +283,7 @@ func init() {
 				MaxLifetime: internal.Duration{
 					Duration: 0,
 				},
+				IsPgBouncer: false,
 			},
 		}
 	})

plugins/inputs/postgresql_extensible/postgresql_extensible_test.go

@@ -17,6 +17,7 @@ func queryRunner(t *testing.T, q query) *testutil.Accumulator {
 				"host=%s user=postgres sslmode=disable",
 				testutil.GetLocalHost(),
 			),
+			IsPgBouncer: false,
 		},
 		Databases: []string{"postgres"},
 		Query:     q,