Initial setup of the CloudEvents Plugin

[ShrutiC-git]

Here's what has been done inside this PR:

1. Add Global-Configuration to this Plugin.
   • Users can enter and save configuration globally; config included sink URL and the corresponding event it will receive.
2. Implement RunListener to listen for runs of a job
   • This implementation will listen to status change of a run for a particular job and notify the sinks accordingly.
3. Construct payload to be sent to the sink and convert this Java object to JSON-string.
4. Wrap the payload inside CloudEvent's binary format and implement Message-Writers to write the CloudEvent to HTTP request.
5. Send request over to the configured Sink with CloudEvent-required headers.

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