Register postgre driver in pkg/event/target (#6689)

Commit 5c13765168 removed postgre registration triggerd
by the automatic gofmt command but it was the only where pg is registered. This commit
fixes behavior and adds unit tests to check whether postgre & sql are registered or not.

vendor/github.com/lib/pq/user_windows.go

@@ -0,0 +1,27 @@
+// Package pq is a pure Go Postgres driver for the database/sql package.
+package pq
+
+import (
+	"path/filepath"
+	"syscall"
+)
+
+// Perform Windows user name lookup identically to libpq.
+//
+// The PostgreSQL code makes use of the legacy Win32 function
+// GetUserName, and that function has not been imported into stock Go.
+// GetUserNameEx is available though, the difference being that a
+// wider range of names are available.  To get the output to be the
+// same as GetUserName, only the base (or last) component of the
+// result is returned.
+func userCurrent() (string, error) {
+	pw_name := make([]uint16, 128)
+	pwname_size := uint32(len(pw_name)) - 1
+	err := syscall.GetUserNameEx(syscall.NameSamCompatible, &pw_name[0], &pwname_size)
+	if err != nil {
+		return "", ErrCouldNotDetectUsername
+	}
+	s := syscall.UTF16ToString(pw_name)
+	u := filepath.Base(s)
+	return u, nil
+}