Document sort_param and drop_param

README.md

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 )
 ```
 
+* `:drop_param` – see [sorting-and-deleting-from-many-collections](https://hexdocs.pm/ecto/3.11.2/Ecto.Changeset.html#cast_assoc/3-sorting-and-deleting-from-many-collections).
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+* `:sort_param` – see [sorting-and-deleting-from-many-collections](https://hexdocs.pm/ecto/3.11.2/Ecto.Changeset.html#cast_assoc/3-sorting-and-deleting-from-many-collections).
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+* `:default_type_on_sort_create` – in some cases, [`sort` creates a new entry](https://github.com/elixir-ecto/ecto/blob/v3.11/test/ecto/changeset/embedded_test.exs#L464); this option specifies which type to use by default for the entry.
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 ### PolymorphicEmbed Ecto type
 
 The `:types` option for the `PolymorphicEmbed` custom type contains a keyword list mapping an atom representing the type