Indices API: fixes GET Alias API backwards compatibility

For just the case when only the aliases are requested, the default indices options are to ignore missing indexes. When requesting any other feature or any combination of features, the default will be to error on missing indices.

Closes #7793
I wonder if this specific default should only be used in the REST layer, or if we should move this logic to the transport action so that it's applied to the java client as well. That way we would have consistency between REST and transport layer...