Skip S3 objects that have been archived to glacier

[yaauie]

When a bucket contains objects that have been archived to glacier, they will be present in the listing, but will have a storage_class of "GLACIER" and attempts to retrieve them will yield 4XX error responses, crashing the plugin.

This PR causes the input to skip objects that have been archived to glacier, emitting a clear message at debug-level.

SEE:

• https://discuss.elastic.co/t/logstash-s3-inout-plugin-crashes-when-reading-glacier-object/141822
• https://discuss.elastic.co/t/s3-input-plugin-failed-to-stream-from-glaciers/143391
• https://discuss.elastic.co/t/s3-input-plugin-choking-on-glacier-files/28119