Use DeliveryGuarantee enum as sink configuration

[fyang86]

Problem description
Flink has already provided a enum DeliveryGuarantee to describe the delivery guarantee that our sink uses. We should leverage it instead of the current PravegaWriterMode enum.

Problem location
PravegaWriterMode, Sink

Suggestions for an improvement

[crazyzhou]

For this task, we need to mark the writer mode API deprecated, and keep its compatibility for this release for now. We will consider removing the writer mode in the next one or two releases.

[crazyzhou]

As the new Sink API is still marked experimental, we decide not changing the old Sink API to keep the compatibility, and directly change to use the DeliveryGuarantee and remove the writer mode support in the new Sink API.