Take into account _default_ mapping in index template when parsing alias filter in index templates.

By also taking into account the type for an index request that indexes into index that doesn't exist in the automatic create index request, the mapping for the new type will take over the `_default_` mapping. Alias filters that then point to fields in the `_default_` mapping will then not fail. 

PR for #8473
can we maybe un-chain this line it's very hard to read... like

```Java
CreateIndexRequest indexReq = new CreateIndexRequest(request);
indexReq.mapping(request.type());
//...
```