**Description**

Currently we have an operator, S3KeySensor which polls for the given prefix in the bucket. At times, there is need to poll for multiple prefixes in given bucket in one go. To have that - I propose to have a S3MultipleKeysSensor, which would poll for multiple prefixes in the given bucket in one go.

**Use case / motivation**

To make it easier for users to poll multiple S3 prefixes in a given bucket.

**Are you willing to submit a PR?**

Yes, I have an implementation ready for that.

**Related Issues**

NA

airflow/providers/amazon/aws/sensors/s3_prefix.py
"""
    Waits for a prefix to exist. A prefix is the first part of a key,
    thus enabling checking of constructs similar to glob ``airfl*`` or
    SQL LIKE ``'airfl%'``. There is the possibility to precise a delimiter to
    indicate the hierarchy or keys, meaning that the match will stop at that
    delimiter. Current code accepts sane delimiters, i.e. characters that
    are NOT special characters in the Python regex engine.
    :param bucket_name: Name of the S3 bucket
    :type bucket_name: str
    :param prefix: The prefix being waited on. Relative path from bucket root level.
    :type prefix: str
    :param delimiter: The delimiter intended to show hierarchy.
        Defaults to '/'.
    :type delimiter: str
    :param aws_conn_id: a reference to the s3 connection
    :type aws_conn_id: str
    :param verify: Whether or not to verify SSL certificates for S3 connection.
        By default SSL certificates are verified.
        You can provide the following values:
        - ``False``: do not validate SSL certificates. SSL will still be used
                 (unless use_ssl is False), but SSL certificates will not be
                 verified.
        - ``path/to/cert/bundle.pem``: A filename of the CA cert bundle to uses.
                 You can specify this argument if you want to use a different
                 CA cert bundle than the one used by botocore.
    :type verify: bool or str
    """
    template_fields = ('prefix', 'bucket_name')
    def __init__(