Added Opsgenie Support

[caronc]

Description:

Related issue (if applicable): n/a

Setup

• Signup @ https://www.opsgenie.com
• Generate your API Key

Syntax

Knowing this, you can build your Opsgenie URL as follows:

• opsgenie://{apikey}/
• opsgenie://{apikey}/@{user}
• opsgenie://{apikey}/*{schedule}
• opsgenie://{apikey}/^{escalation}
• opsgenie://{apikey}/#{team}

You can mix and match what you want to notify freely

• opsgenie://{apikey}/@{user}/#{team}/*{schedule}/^{escalation}

New Service Completion Status

• apprise/plugins/NotifyOpsgenie.py
• setup.py
  • add new service into the keywords section of the setup() declaration
• README.md
  • add entry for new service to table (as a quick reference)
• packaging/redhat/python-apprise.spec
  • add new service into the %global common_description

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• No lint errors (use flake8)
• 100% test coverage