Cherry-pick #17858 to 7.x: Moved stream.* fields to top of event

[michalpristas]

Cherry-pick of PR #17858 to 7.x branch. Original message:

What does this PR do?

Modifies generated add_fields processor to include stream fields to top level not under fields.*

Why is it important?

It is required

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.

[elasticmachine]

Pinging @elastic/ingest-management (Project:fleet)

[ph]

LGTM, will restart CI everything is red, but this is not related to this PR its really the CI environment.

[ph]

Jenkins test this please