mails: make error reporting by mail work with secure mail servers

Even with Kallithea mails working, TurboGears / backlash error reporting would
fail like:

Error while reporting exception with <backlash.tracing.reporters.mail.EmailReporter object at 0x7f8f986f8710>
Traceback (most recent call last):
File ".../env/lib/python3.7/site-packages/backlash/tracing/reporters/mail.py", line 49, in report
result = server.sendmail(self.from_address, self.error_email, msg.as_string())
File "/usr/lib64/python3.7/smtplib.py", line 867, in sendmail
raise SMTPSenderRefused(code, resp, from_addr)
smtplib.SMTPSenderRefused: (530, b'5.7.0 Must issue a STARTTLS command first.', 'kallithea@example.com')

Extend the .ini template to forward all the mail settings described on
https://turbogears.readthedocs.io/en/latest/reference/config-options.html#error-reporting