Report client name as entity to OpsGenie

[steti]

Pull Request Checklist

Is this in reference to an existing issue? No

General

• [x] Update Changelog following the conventions laid out on Keep A Changelog
• [ ] Update README with any necessary configuration snippets Not necessary
• [ ] Binstubs are created if needed Not necessary
• [x] RuboCop passes
• [ ] Existing tests pass No existing tests

  New Plugins

• [ ] Tests
• [ ] Add the plugin to the README
• [ ] Does it have a complete header as outlined here

  Purpose

Report the Sensu client name as the entity to OpsGenie. The OpsGenie alert API defines entity as:

The entity the alert is related to.

This is useful in the OpsGenie advanced integration settings in order to, for example, automatically generate a link to a runbook or other documentation based on the client name.

Known Compatablity Issues

[eheydrick]

👍 Thanks @steti!