Improve the plugins

[andromedarabbit]

• Empty record should not be sent to DataDog
• source, sourcecategory, and custom categories can be set

What does this PR do?

A brief description of the change being made with this pull request.

Motivation

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Additional Notes

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[diclophis]

@estib / DataDog Tech Support in general...

Having some movement on this PR would greatly help our integration which we are still evaluating before purchasing...

[NBParis]

Hello @andromedarabbit and @diclophis ,

Sorry for the delay here and thanks for helping us improving Datadog. I'll make sure this is reviewed shortly.

Thanks, Nils

[andromedarabbit]

@ajacquemot Added a few details into README.md.

[ajacquemot]

Thanks @andromedarabbit for your very nice work, I'll publish a new version of the plugin along with the remaining open PRs.