feat: create detour notification table

[firestack]

Asana Ticket: https://app.asana.com/0/0/1208312289539633/f

Not sure if this PR is too small, but I'm fairly certain this will be the final shape of the table and that could be merged first.

This adds a field to the notifications table, because there were errors if it wasn't added, but it's intended that this table is entirely unused as of this PR, following PRs will use this table.

If this PR is too small I can roll this table creation into a PR that uses it.

[github-actions]

Coverage of commit d679f48

Summary coverage rate:
  lines......: 92.5% (3302 of 3571 lines)
  functions..: 71.5% (1365 of 1908 functions)
  branches...: no data found

Files changed coverage rate:
                                                                  |Lines       |Functions  |Branches    
  Filename                                                        |Rate     Num|Rate    Num|Rate     Num
  ======================================================================================================
  lib/notifications/db/detour.ex                                  | 0.0%      3| 0.0%     7|    -      0
  lib/notifications/db/notification.ex                            |66.7%      6|77.8%     9|    -      0

Download coverage report

[hannahpurcell]

Not too small! Looks good 👍