Add KV destination plugin

Problem/Motivation

In some cases source data needs to be private. We can do that with the File destination but what if we don't want it on the disk?

Steps to reproduce

N/A

Proposed resolution

Add a KV destination plugin.

Remaining tasks

• Discussion.
• Patch.
• Commit.
• Rejoicing.

User interface changes

A new destination plugin.

API changes

API addition

Data model changes

None.