Support SNS HTTPS as a Source

Provide an SNS Source which can subscribe to an SNS topic (or use an existing subscription) to receive SNS notifications over HTTP/S.

This will be similar to the existing HTTP source plugin. However, it should also support auto confirmation of subscription requests. When an expected topic names a request, visit the SubscribeURL per the SNS protocol.

This can support auto-subscription either by a list of topics or using a topic name pattern.

Provide two options for topic auto-confirmation:

• topics - A list of topics to auto-confirm
• topics_regex - A list of regex patterns. Any topic matching will auto-confirm.

Provide configuration options just like http source:

• port
• path
• request_timeout
• thread_count
• max_connection_count
• max_pending_requests
• ssl
• ssl_certificate_file
• ssl_key_file
• use_acm_certificate_for_ssl
• acm_certificate_arn
• acm_private_key_password
• acm_certificate_timeout_millis
• aws_region