Change fixed organization id to fixed organization slug (#15067)

* Remove hard coded organization id from seed

Since we create (hopefully) an organization with a known slug, use
find_by here to set the organization_id on the seeded DisplayAd.

* Since the DisplayAd looks by slug, create org if slug not found

Change the seed guard to ensure an organization with slug "bachmanity"
is present - we'll find by slug in DisplayAd (rather than assuming
this is id 1).

spec/support/seeds/seeds_e2e.rb

@@ -88,7 +88,7 @@ end
 
 ##############################################################################
 
-seeder.create_if_none(Organization) do
+seeder.create_if_doesnt_exist(Organization, "slug", "bachmanity") do
   organization = Organization.create!(
     name: "Bachmanity",
     summary: Faker::Company.bs,
@@ -626,8 +626,9 @@ end
 ##############################################################################
 
 seeder.create_if_none(DisplayAd) do
+  org_id = Organization.find_by(slug: "bachmanity").id
   DisplayAd.create!(
-    organization_id: 1,
+    organization_id: org_id,
     body_markdown: "<h1>This is an add</h1>",
     placement_area: "sidebar_left",
     published: true,