Bug 30646: Add welcome email support to SAML2

Bug 30646: Add welcome email support to SAML2

This patch adds the ability to enable the welcome email notice for new
users added via the Shibboleth autocreate option.

Test plan
1) Configure Shibboleth for authentication
2) Enable the welcome email by adding '<welcome>1</welcome>' to your
   shibboleth config block
3) Confirm you have autocreate enabled for your Shibboleth config
4) Attempt to login with an entirely new user to Koha using the shibboleth
   connection (with a user who has a valid email address mapped to Koha
   borrower fields)
5) Confirm the email is sent by looking at the notices for the new user.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>