**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!

#include <Columns/ColumnLowCardinality.h>
#include <Interpreters/Context.h>
namespace DB
{
namespace ErrorCodes
{
    extern const int ATTEMPT_TO_READ_AFTER_EOF;
    extern const int CANNOT_PARSE_NUMBER;
    extern const int CANNOT_READ_ARRAY_FROM_TEXT;
    extern const int CANNOT_PARSE_INPUT_ASSERTION_FAILED;
    extern const int CANNOT_PARSE_QUOTED_STRING;
    extern const int CANNOT_PARSE_ESCAPE_SEQUENCE;
    extern const int CANNOT_PARSE_DATE;
    extern const int CANNOT_PARSE_DATETIME;
    extern const int CANNOT_PARSE_TEXT;
    extern const int CANNOT_PARSE_UUID;
    extern const int TOO_FEW_ARGUMENTS_FOR_FUNCTION;
    extern const int LOGICAL_ERROR;
    extern const int TYPE_MISMATCH;
    extern const int CANNOT_CONVERT_TYPE;
    extern const int ILLEGAL_COLUMN;
    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
    extern const int ILLEGAL_TYPE_OF_ARGUMENT;
    extern const int NOT_IMPLEMENTED;
    extern const int CANNOT_INSERT_NULL_IN_ORDINARY_COLUMN;
}
/** Type conversion functions.
  * toType - conversion in "natural way";
  */
inline UInt32 extractToDecimalScale(const ColumnWithTypeAndName & named_column)