**Describe what's wrong**

It's not possible to use digit as tuple name, so it's not possible to parse JSON files to nested tuple structure with JSONExtract.

**Does it reproduce on recent release?**

Yes

ClickHouse 21.12


**How to reproduce**
```
WITH
    '{"1":{"key":"value"}}' AS data,
    JSONExtract(data, 'Tuple("1" Tuple(key String))') AS parsed_json
SELECT parsed_json AS ssid

Query id: 5bc7b6cf-155a-421c-ac20-f3be09bd9692


0 rows in set. Elapsed: 0.003 sec.

Received exception from server (version 21.12.1):
Code: 36. DB::Exception: Received from localhost:9000. DB::Exception: Explicitly specified names of tuple elements cannot start with digit: While processing JSONExtract('{"1":{"key":"value"}}' AS data, 'Tuple("1" Tuple(key String))') AS ssid. (BAD_ARGUMENTS)
```

**Expected behavior**

It's possible to parse JSON with digit keys.


{
    SerializationTuple::ElementSerializations serializations(elems.size());
    const auto & info_tuple = assert_cast<const SerializationInfoTuple &>(info);
    for (size_t i = 0; i < elems.size(); ++i)
    {
        String elem_name = have_explicit_names ? names[i] : toString(i + 1);
        auto serialization = elems[i]->getSerialization(*info_tuple.getElementInfo(i));
        serializations[i] = std::make_shared<SerializationNamed>(serialization, elem_name);
    }
    return std::make_shared<SerializationTuple>(std::move(serializations), have_explicit_names);
}
MutableSerializationInfoPtr DataTypeTuple::createSerializationInfo(const SerializationInfo::Settings & settings) const
{
    MutableSerializationInfos infos;
    infos.reserve(elems.size());
    for (const auto & elem : elems)
        infos.push_back(elem->createSerializationInfo(settings));
    return std::make_shared<SerializationInfoTuple>(std::move(infos), settings);
}
static DataTypePtr create(const ASTPtr & arguments)