set default value of kafka version to 2.1.0

[khushijain21]

This sets default value of kafka version to 2.1.0

Closes #41474

[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 @khushijain21? 🙏.
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-8./d is the label to automatically backport to the 8./d branch. /d is the digit

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @khushijain21? 🙏.
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-8./d is the label to automatically backport to the 8./d branch. /d is the digit

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[khushijain21]

@pierrehilbert we don't to backport this to 8.X correct? And this will be introduced in 9.0. Let me know

[pierrehilbert]

Correct, we shouldn't backport this to 8.x branch.

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b kafka-min-version upstream/kafka-min-version
git merge upstream/main
git push upstream kafka-min-version

[rdner]

@faec I'm afraid I can miss some required changes elsewhere, could you please have a quick look?