Add image processing and generate blurhash for server thumbnail (#19348)

Remove separate server hero setting

db/migrate/20221012181003_add_blurhash_to_site_uploads.rb

@@ -0,0 +1,5 @@
+class AddBlurhashToSiteUploads < ActiveRecord::Migration[6.1]
+  def change
+    add_column :site_uploads, :blurhash, :string
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2022_10_06_061337) do
+ActiveRecord::Schema.define(version: 2022_10_12_181003) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -866,6 +866,7 @@ ActiveRecord::Schema.define(version: 2022_10_06_061337) do
     t.json "meta"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.string "blurhash"
     t.index ["var"], name: "index_site_uploads_on_var", unique: true
   end