Document Destroy Async (#41680)

* Document Destroy Async
Motivation:
  - Add docs for Destroy async. I think I probably need to add
    information about setting up active job, but I am not sure where we
    want this, so I am putting this together to start conversation.

Related Issues:
  - #41093

* Active Job not ActiveJob

* Fix some spelling issues

[Cory Gwin, Rafael Mendonça França, Eileen M. Uchitelle, Henrik Nyh]

guides/source/association_basics.md

@@ -1011,6 +1011,9 @@ If you set the `:dependent` option to:
 associated objects.
 * `:delete`, when the object is destroyed, all its associated objects will be
 deleted directly from the database without calling their `destroy` method.
+* `:destroy_async`: when the object is destroyed, an `ActiveRecord::DestroyAssociationAsyncJob`
+job is enqueued which will call destroy on its associated objects. Active Job must be set up
+for this to work.
 
 WARNING: You should not specify this option on a `belongs_to` association that is connected with a `has_many` association on the other class. Doing so can lead to orphaned records in your database.
 
@@ -1312,6 +1315,7 @@ Controls what happens to the associated object when its owner is destroyed:
 
 * `:destroy` causes the associated object to also be destroyed
 * `:delete` causes the associated object to be deleted directly from the database (so callbacks will not execute)
+* `:destroy_async`: when the object is destroyed, an `ActiveRecord::DestroyAssociationAsyncJob` job is enqueued which will call destroy on its associated objects. Active Job must be set up for this to work.
 * `:nullify` causes the foreign key to be set to `NULL`. Polymorphic type column is also nullified on polymorphic associations. Callbacks are not executed.
 * `:restrict_with_exception` causes an `ActiveRecord::DeleteRestrictionError` exception to be raised if there is an associated record
 * `:restrict_with_error` causes an error to be added to the owner if there is an associated object
@@ -1632,7 +1636,7 @@ The [`collection.clear`][] method removes all objects from the collection accord
 @author.books.clear
 ```
 
-WARNING: Objects will be deleted if they're associated with `dependent: :destroy`,
+WARNING: Objects will be deleted if they're associated with `dependent: :destroy` or `dependent: :destroy_async`,
 just like `dependent: :delete_all`.
 
 ##### `collection.empty?`
@@ -1768,6 +1772,7 @@ Controls what happens to the associated objects when their owner is destroyed:
 
 * `:destroy` causes all the associated objects to also be destroyed
 * `:delete_all` causes all the associated objects to be deleted directly from the database (so callbacks will not execute)
+* `:destroy_async`: when the object is destroyed, an `ActiveRecord::DestroyAssociationAsyncJob` job is enqueued which will call destroy on its associated objects. Active Job must be set up for this to work.
 * `:nullify` causes the foreign key to be set to `NULL`. Polymorphic type column is also nullified on polymorphic associations. Callbacks are not executed.
 * `:restrict_with_exception` causes an `ActiveRecord::DeleteRestrictionError` exception to be raised if there are any associated records
 * `:restrict_with_error` causes an error to be added to the owner if there are any associated objects