`log_level` type should be `Union[str, int]` and not just `str`

[gioruffa]

Hello there,
First of all: thanks a lot for the great library. It has sensibly improved our life when writing custom resources.

I have found a small inconsistency in the type hints for the CfnResource's log_level constructor parameter.

Current behavior

Version affected: main branch f2095c5

CfnResource constructor specifies that log_level should be a string.
In practice though, the log_level is used in log_helper.py to set the log level on the root logger in the stdlib logging module.

    logging.root.setLevel(level)

The logging module supports both string and integers to specify the log level. As a matter of fact, the log level is stored internally as an integer. The string is translated to an int using the _checkLevel method:

def _checkLevel(level):
    if isinstance(level, int):
        rv = level
    elif str(level) == level:
        if level not in _nameToLevel:
            raise ValueError("Unknown level: %r" % level)
        rv = _nameToLevel[level]
    else:
        raise TypeError("Level not an integer or a valid string: %r" % level)
    return rv

Expected behavior

log_level type hint should support both string and int.

Contribution

I am more than happy to create a PR to fix this, provided that you think it should be fixed.