[WIP] Delete all records matching a query

Sorry, I'm having a bit of trouble digging through the code.

I think that this basic structure is correct for adding this functionality, but I'm unsure what to write in the `update_delete_all` method. Should it update some flag in the `request_options` `hash_storage`?

After that, where is the code that actually sends the request to ES? Will need to have it check for the new delete flag and send a DELETE request if it is true.
As you can see - https://github.com/toptal/chewy/blob/436d47650e320ffb5c3b5978e176b92253ebe1ad/lib/chewy/query/compose.rb#L26 it returns empty hash, so just do something like:

```
def delete_all_request_body
  { body: _filtered_query(_request_query, _request_filter, options.slice(:strategy)).presence || { query: { } } }
end
```