Cherry-pick #18967 to 7.x: Moved from stream to dataset

[michalpristas]

Cherry-pick of PR #18967 to 7.x branch. Original message:

What does this PR do?

Changes injected processor to events so it enriches them with dataset.* instead of stream.*

Why is it important?

elastic/package-registry#491

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

As draft until we are ready and in sync to merge

Fixes: elastic/package-registry#491
Fixes: #18826

cc @ruflin

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request #19093 opened]

• Start Time: 2020-06-10T09:30:40.006+0000

• Duration: 34 min 21 sec

[ruflin]

LGTM. Did not test it locally but assume it is a 1 to 1 cherry pick.