Update plugin description

[dblock]

Coming from opensearch-project/opensearch-plugins#92.

Each plugin has a short descriptive text blurb that says what it does: this appears in plugin-descriptor.properties (OpenSearch plugins) or package.json (OpenSearch Dashboards plugins), as well as on the project website's "source" page and in the "About" section of every repo. These were created one-by-one over the years as plugins were created, so looking at them all together now it would be hard for somebody new to the project to use these to understand what the plugins do.

[jcgraybill]

Description to use: Run queries in the background and retrieve partial results along the way.

[elfisher]

This is complete. Closing the issue.