Fixes for post-merged feedback on 'Announcement Created By You' notification

Added 'Announcement Reply' to notification_types.yml

Removed 'Announcement Reply' from category and category description.
since it is combined with 'Announcement Created By You' in the
notification settings.

Changed 'Announcement Created' to 'Announcement Created By You' in
default frequency. This fixes a bug where the default was set to daily
instead of never
Fixes CNVS-15951

Test Plan:

- With a user who has never set the 'Announcement Created By You'
  Check that 'Announcement Created By You' defaults to nothing

- Check that 'Announcement Created By You' and 'Announcement Reply'
  still function correctly

Change-Id: I7d0894539d34d2588c18394f54cffd84b6db86a2
Reviewed-on: https://gerrit.instructure.com/42076
Reviewed-by: Joel Hough <joel@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>