**Describe the bug**
When using the HTTP protocol with DateTime64 types, numerical timestamps in milliseconds do not parse correctly. This is an issue when using the Clickhouse JDBC driver with Avro Kafka records because the timestamps are integers. 

**How to reproduce**
I'm using the following CH version: yandex/clickhouse-server:20.4.5.36

Create a sample table with: 
```sql
create table tst(ts DateTime64(3)) engine TinyLog();
```

Attempt to insert millisecond timestamp into the column:
```bash
echo "1596215121682" | http -v :8123 query=="insert into tst format TSV"
```

Error:
```bash
Code: 27, e.displayText() = DB::Exception: Cannot parse input: expected '\n' before: '682\n': (at row 1)

Row 1:
Column 0,   name: ts, type: DateTime64(3), parsed text: "1596215121"
ERROR: garbage after DateTime64(3): "682<LINE FEED>"

 (version 20.4.5.36 (official build))
```

Oddly, specifying a raw query, this works:
```bash
echo 'insert into tst values(1596215121682)' | curl 'http://localhost:8123/' --data-binary @-
```
Result:
```bash
SELECT *
FROM tst

┌──────────────────────ts─┐
│ 2020-07-31 17:05:21.682 │
└─────────────────────────┘
```



**Expected behavior**
I expect to be able to insert integer millisecond timestamps using the HTTP batch insert protocol. 

Again, this issue is preventing us from using the Clickhouse JDBC driver because it fails to parse our Avro records from Kafka.

Appreciate the help!

static constexpr auto accurate_cast_or_null_name = "accurateCastOrNull";
    static constexpr auto cast_name = "CAST";
    static constexpr auto name = cast_type == CastType::accurate
        ? accurate_cast_name
        : (cast_type == CastType::accurateOrNull ? accurate_cast_or_null_name : cast_name);
    static FunctionOverloadResolverImplPtr create(const Context & context)
    {
        return createImpl(context.getSettingsRef().cast_keep_nullable);
    }
    static FunctionOverloadResolverImplPtr createImpl(bool keep_nullable, std::optional<Diagnostic> diagnostic = {})
    {
        return std::make_unique<CastOverloadResolver>(keep_nullable, std::move(diagnostic));
    }
    explicit CastOverloadResolver(bool keep_nullable_, std::optional<Diagnostic> diagnostic_ = {})
        : keep_nullable(keep_nullable_), diagnostic(std::move(diagnostic_))
    {}
    String getName() const override { return name; }
    size_t getNumberOfArguments() const override { return 2; }
    ColumnNumbers getArgumentsThatAreAlwaysConstant() const override { return {1}; }
protected:
    FunctionBaseImplPtr build(const ColumnsWithTypeAndName & arguments, const DataTypePtr & return_type) const override
    {
        DataTypes data_types(arguments.size());
        for (size_t i = 0; i < arguments.size(); ++i)
            data_types[i] = arguments[i].type;
        auto monotonicity = MonotonicityHelper::getMonotonicityInformation(arguments.front().type, return_type.get());
        return std::make_unique<FunctionCast>(name, std::move(monotonicity), data_types, return_type, diagnostic, cast_type);
    }
    DataTypePtr getReturnType(const ColumnsWithTypeAndName & arguments) const override
    {