Add account migration UI (#11846)

Fix #10736

- Change data export to be available for non-functional accounts
- Change non-functional accounts to include redirecting accounts

app/models/concerns/account_associations.rb

@@ -52,6 +52,8 @@ module AccountAssociations
 
     # Account migrations
     belongs_to :moved_to_account, class_name: 'Account', optional: true
+    has_many :migrations, class_name: 'AccountMigration', dependent: :destroy, inverse_of: :account
+    has_many :aliases, class_name: 'AccountAlias', dependent: :destroy, inverse_of: :account
 
     # Hashtags
     has_and_belongs_to_many :tags