Add DefaultValue attribute to Kafka trigger attribute's IsBatched prop

[satvu]

Issue describing the changes in this PR

resolves #2140

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)

Locally tested - cardinality is correctly populated in source-generated function metadata with this change.

[liliankasem]

Is this a breaking change? Will this change the default behaviour of the kafka attribute?

Please also update release notes and ext version

[satvu]

Is this a breaking change? Will this change the default behaviour of the kafka attribute?

Please also update release notes and ext version

Added - this is not breaking or changing the default behavior because the DefaultValue attribute's value matches the one set here earlier in the file.