Disable sending confirmation email when 3pid is disabled #14682 (#14725)

* Fixes #12277 :Disable sending confirmation email when 3pid is disabled

* Fix test_add_email_if_disabled test case to reflect changes to enable_3pid_changes flag

* Add changelog file

* Rename newsfragment.

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>