Allow the use of the Intelligent-Tiering storage class

[JPLachance]

A long time ago, AWS released the Intelligent-Tiering storage class.

To use it, all we need is to set an Object storage class to INTELLIGENT_TIERING. Doing it on object upload saves us a lifecycle transition.

Today, the list of valid storage classes accepted by the S3 output plugin does not contain INTELLIGENT_TIERING.

Therefore, the S3 output plugin is rejecting our configuration.

Can we add INTELLIGENT_TIERING to the list of valid storage classes we can use in the S3 output plugin?

If yes, I can open a pull request.

Thanks!