smtplib documentation fixes (GH-8708)


* SMTP.startssl: Fix doc on keyfile and certfile use

* SMTP.startssl: Add missing keyfile and certfile deprecation notice

* SMTP: Doc grammar fixes
(cherry picked from commit da12063f2f53b7d272824863ed24260cefb22e8c)

Co-authored-by: Ville Skyttä <ville.skytta@iki.fi>
1 file changed