Add Data.ContentType for Cloud Events #2260

[thompson-tomo]

Fixes #2260

Changes

Enables capturing of data content type for cloud events.

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Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.