**Describe the bug**
Here's my table:
```sql
CREATE TABLE table2
(
        EventDate Date,
        Id Int32,
        Value Int32
)
Engine = MergeTree()
PARTITION BY toYYYYMM(EventDate)
ORDER BY Id;
```

Modify default value (intentionally wrong):
```
>>> alter table table2 modify column Value default 'some_string';

ALTER TABLE table2
    MODIFY COLUMN `Value` DEFAULT 'some_string'

Ok.

0 rows in set. Elapsed: 0.007 sec. 
```

Now you obviously cannot insert anything to this table, because:
```
>>> insert into table2 (EventDate, Id) values (1234567890, 2)

INSERT INTO table2 (EventDate, Id) VALUES

Received exception from server (version 20.9.3):
Code: 6. DB::Exception: Received from localhost:9000. DB::Exception: Cannot parse string 'some_string' as Int32: syntax error at begin of string. Note: there are toInt32OrZero and toInt32OrNull functions, which returns zero/NULL instead of throwing exception.. 

1 rows in set. Elapsed: 0.002 sec. 
```

**How to reproduce**
* Which ClickHouse server version to use: 20.9.3
* Which interface to use, if matters: I used standard CLI

**Expected behavior**
Currently ClickHouse doesn't check types compability while setting a DEFAULT value for a column. Maybe ClickHouse should validate DEFAULT values for type compability?

{
    MutationCommand command;
    auto ast = std::make_shared<ASTAlterCommand>();
    ast->type = ASTAlterCommand::MATERIALIZE_TTL;
    command.type = MutationCommand::MATERIALIZE_TTL;
    command.ast = std::move(ast);
    return command;
}
MutationCommands AlterCommands::getMutationCommands(StorageInMemoryMetadata metadata, bool materialize_ttl, const Context & context) const
{
    MutationCommands result;
    for (const auto & alter_cmd : *this)
        if (auto mutation_cmd = alter_cmd.tryConvertToMutationCommand(metadata, context); mutation_cmd)
            result.push_back(*mutation_cmd);
    if (materialize_ttl)
    {
        for (const auto & alter_cmd : *this)
        {
            if (alter_cmd.isTTLAlter(metadata))
            {
                result.push_back(createMaterializeTTLCommand());
                break;
            }
        }
    }
    return result;
}
}