**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!

struct NameToUInt8 { static constexpr auto name = "toUInt8"; };
struct NameToUInt16 { static constexpr auto name = "toUInt16"; };
struct NameToUInt32 { static constexpr auto name = "toUInt32"; };
struct NameToUInt64 { static constexpr auto name = "toUInt64"; };
struct NameToUInt256 { static constexpr auto name = "toUInt256"; };
struct NameToInt8 { static constexpr auto name = "toInt8"; };
struct NameToInt16 { static constexpr auto name = "toInt16"; };
struct NameToInt32 { static constexpr auto name = "toInt32"; };
struct NameToInt64 { static constexpr auto name = "toInt64"; };
struct NameToInt128 { static constexpr auto name = "toInt128"; };
struct NameToInt256 { static constexpr auto name = "toInt256"; };
struct NameToFloat32 { static constexpr auto name = "toFloat32"; };
struct NameToFloat64 { static constexpr auto name = "toFloat64"; };
struct NameToUUID { static constexpr auto name = "toUUID"; };
using FunctionToUInt8 = FunctionConvert<DataTypeUInt8, NameToUInt8, ToNumberMonotonicity<UInt8>>;
using FunctionToUInt16 = FunctionConvert<DataTypeUInt16, NameToUInt16, ToNumberMonotonicity<UInt16>>;
using FunctionToUInt32 = FunctionConvert<DataTypeUInt32, NameToUInt32, ToNumberMonotonicity<UInt32>>;
using FunctionToUInt64 = FunctionConvert<DataTypeUInt64, NameToUInt64, ToNumberMonotonicity<UInt64>>;
using FunctionToUInt256 = FunctionConvert<DataTypeUInt256, NameToUInt256, ToNumberMonotonicity<UInt256>>;
using FunctionToInt8 = FunctionConvert<DataTypeInt8, NameToInt8, ToNumberMonotonicity<Int8>>;
using FunctionToInt16 = FunctionConvert<DataTypeInt16, NameToInt16, ToNumberMonotonicity<Int16>>;
using FunctionToInt32 = FunctionConvert<DataTypeInt32, NameToInt32, ToNumberMonotonicity<Int32>>;
using FunctionToInt64 = FunctionConvert<DataTypeInt64, NameToInt64, ToNumberMonotonicity<Int64>>;
using FunctionToInt128 = FunctionConvert<DataTypeInt128, NameToInt128, ToNumberMonotonicity<Int128>>;
using FunctionToInt256 = FunctionConvert<DataTypeInt256, NameToInt256, ToNumberMonotonicity<Int256>>;
using FunctionToFloat32 = FunctionConvert<DataTypeFloat32, NameToFloat32, ToNumberMonotonicity<Float32>>;
using FunctionToFloat64 = FunctionConvert<DataTypeFloat64, NameToFloat64, ToNumberMonotonicity<Float64>>;
using FunctionToDate = FunctionConvert<DataTypeDate, NameToDate, ToDateMonotonicity>;
using FunctionToDateTime = FunctionConvert<DataTypeDateTime, NameToDateTime, ToDateTimeMonotonicity>;
using FunctionToDateTime32 = FunctionConvert<DataTypeDateTime, NameToDateTime32, ToDateTimeMonotonicity>;