Adds custom message format.

[tavilarion]

Pull Request Checklist

Is this in reference to an existing issue?

General

• [ ] Update Changelog following the conventions laid out on Keep A Changelog

• [ ] Update README with any necessary configuration snippets

• [ ] Binstubs are created if needed

• [ ] RuboCop passes

• [ ] Existing tests pass

New Plugins

• [ ] Tests

• [ ] Add the plugin to the README

• [ ] Does it have a complete header as outlined here

Purpose

Known Compatability Issues

[majormoses]

@eheydrick ping since I know you use opsgenie.

[majormoses]

Thanks for your contribution to Sensu plugins! Without people like you submitting PRs we couldn't run the project. I will review it shortly.

[tavilarion]

Changed the option to receive the path to a ERB template, please let me know what you think.

[tavilarion]

Fixed the changelog.

[majormoses]

will give it a day and see if @eheydrick has any thoughts since he uses this.

[tavilarion]

Thanks for the prompt response guys 👍

[majormoses]

Alright looks like we are gonna just merge this. @eheydrick whenever you are back you should probably retroactively review.

[majormoses]

released: https://rubygems.org/gems/sensu-plugins-opsgenie/versions/3.1.0