### Description

This is to investigate what we could do to support the data streams in SQL. The backing indices can be queried already, but to address them similarly as they're queried over QDSL one would need to construct a pattern learned out of band and not through SQL metadata discovery mechanisms.
x-pack/plugin/ql/src/main/java/org/elasticsearch/xpack/ql/index/IndexResolver.java
if (fieldCap.isSearchable() && fieldCap.nonSearchableIndices() != null) {
                    if (errorMessage.length() > 0) {
                        errorMessage.append(",");
                    }
                    errorMessage.append("mapped as searchable except in ");
                    errorMessage.append(Arrays.toString(fieldCap.nonSearchableIndices()));
                }
                if (errorMessage.length() > 0) {
                    return new InvalidMappedField(n, errorMessage.toString());
                }
            }
            
            return null;
        });
        if (indices.size() > 1) {
            throw new QlIllegalArgumentException(
                "Incorrect merging of mappings (likely due to a bug) - expect at most one but found [{}]",
                indices.size()
            );
        }
        final String indexName = fieldCapsResponse.getIndices()[0];
        return IndexResolution.valid(indices.isEmpty() ? new EsIndex(indexName, emptyMap()) : indices.get(0));
    }
    private static EsField createField(
        DataTypeRegistry typeRegistry,
        String fieldName,
        Map<String, Map<String, FieldCapabilities>> globalCaps,
        Map<String, EsField> hierarchicalMapping,
        Map<String, EsField> flattedMapping,
        Function<String, EsField> field