Allow storage trigger filters

**Is your feature request related to a problem? Please describe.**

Storage Triggers currently invoke the Lambda function on _any_ `ObjectCreated` or `ObjectRemoved` event. This means that the function will be triggered multiple times for common use cases such as creating an image thumbnail. As part of setup, suggest adding an optional field to specify a custom prefix.

**Describe the solution you'd like**

Allow me to control when a trigger is invoked using the S3 Notification Filter (AWS::S3::Bucket NotificationFilter) or a simplified version that allows me to specify a string prefix.

**Describe alternatives you've considered**

Multiple buckets, one with the trigger and one without, would also be an option but not supported today.