Bug 12802: Update notice_email_address method to return a list

Bug 12802: Update notice_email_address method to return a list

This patch updates the notice_email_address method to return a comma
separated list of addresses as expected by Email::Sender if you wish to
send mail to multiple To addresses.

To test:

1. Install database update and restart services
2. Go to Koha Administration -> system preferences. Search for EmailFieldPrimary. Confirm the options show as checkboxes and you can select multiple.
3. Search for a patron. Put different email addresses in each of the possible email fields (i.e. primary email, secondary email, alternate email).
4. Make sure 'first valid' is checked in EmailFieldPrimary.
5. Go to your patron, click the More dropdown and send a welcome email.
6. In your terminal, go into the database to view the message queue.

sudo koha-mysql instance
select * from message_queue\G

7.  Confirm your welcome email is visible, with ONLY the first valid email in
    the to_address field.
8.  Select other combinations of emails in EmailFieldPrimary.
9.  Send another welcome email to the same patron, then run the message_queue
    SQL query again.
10. Confirm your welcome email is visible and shows all selected addresses
    concatenated by , in the to_address field.
11. Enable KTD to send email [1] (without email configured you will not
    be able to confirm the delivery to multiple addresses).
12. Run misc/cronjobs/process_message_queue.pl to trigger sending the
    queued notices from above.
13. Check that the addresses in the to_address all actually recieve the
    notice.

[1] To test sending emails using a Google account:
    - Set up an App password for your Google Account
    - Configure a new 'SMTP Server' under 'Administration > SMTP servers'
      using the following settings where `User name` = your Google email
      address and `Password` = your APP password, not your Google account
      password):

      Host: smtp.gmail.com
      Port: 587
      Timeout: 120
      SSL: STARTTLS
      User name: GOOGLEACCOUNTUSER
      Password: GOOGLEAPPPASSWORD

    - Set this server as default

Sponsored-by: St Luke's Grammar School & Pymble Ladies' College
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
Signed-off-by: Axelle Clarisse <axelle.clarisse@univ-amu.fr>
Signed-off-by: Mathieu Saby <mathsabypro@gmail.com>
Signed-off-by: Aleisha Amohia <aleisha@catalyst.net.nz>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>