[ML] Change wizard's search query to use match_all

[jgowdyelastic]

In every new job wizard, the search used to retrieve the data for the line chart and for the datafeed's query uses:

"query_string": {
  "analyze_wildcard": true,
   "query": "*"
}

This can hit a problem if the index has index.query.default_field configured to be a field which isn't populated in the majority of documents.
Rather than query_string, the search should use "match_all": {}.

[elasticmachine]

Pinging @elastic/ml-ui