Make botocore.config.Config.{connect,read}_timeout configurable

[k5342]

Allow users to configure botocore.{connect,read}_timeout in pfio.v2.S3. Support both the ways via the custom scheme or via directly passing the initializer (from_url, pfio.v2.S3) like the below:

a) via the custom scheme

[baz]
scheme = s3
endpoint = https://s3.example.com
aws_access_key_id=hoge
aws_secret_access_key=$HOME
connect_timeout=300
read_timeout=120

b) via the initializer (from_url) ... from a test code

def test_s3_init_with_timeouts(s3_fixture):
    with from_url('s3://test-bucket/base',
                  connect_timeout=300,
                  read_timeout=120) as s3:
        assert isinstance(s3, S3)
        assert (s3.botocore_config['connect_timeout'] == 300)
        assert (s3.botocore_config['read_timeout'] == 120)

[sethi0g0]

LGTM :dogeza: