Backport #36055 by @lunny
Replace #36032Fix#36030
This PR use `net/smtp` instead of gomail's smtp. Now
github.com/wneessen/go-mail will be used only for generating email
message body.
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Move all mail sender related codes into a sub package of
services/mailer. Just move, no code change.
Then we just have dependencies on go-mail package in the new sub
package. We can use other package to replace it because it's
unmaintainable. ref #18664
