[docs][filebeat]: add 4th step in migrate-to-filestream

[VihasMakwana]

Proposed commit message

Follow up PR from #39828.

Add a 4th step to enure that the user disables take_over mode once they start receiving events with take_over tag.

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/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @VihasMakwana? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[pierrehilbert]

@VihasMakwana even if Julien & I approved the PR, please wait for @kilfoyle's review to ensure consistency between our docs.

[kilfoyle]

LGTM! 🚀
Just one small suggestion.