Bug 35187: Fix missing line breaks in WELCOME notice

Bug 35187: Fix missing line breaks in WELCOME notice

When a notices is marked as HTML, we need to use block elements
(p, div, li, etc.) or explicit line breaks.
This adds the line breaks where required.

To test:

WELCOME
* Without patch
* Make sure your Koha can send email (set up SMTP server, KohaAdminLibraryAddress)
* Make sure your patron has an email set
* In patron account, use "More > Welcome email"
* Verify all text is on one line
* Apply patch
* reset_all to install new sample notice templates
* Repeat test, verify welcome notice is now nice

(cherry picked from commit d60fe27ea4bda16efcd0db096d756e8a54552056)
Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>