fix(schema-history): make latestVersion field on result optional

[aditya-radhakrishnan]

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub

[github-actions]

Unit Test Results (build & test)

504 tests  ±0   504 ✔️ ±0   8m 40s ⏱️ -30s
117 suites ±0       0 💤 ±0 
117 files   ±0       0 ❌ ±0 

Results for commit c7a8eeb. ± Comparison against base commit e189be7.

[jjoyce0510]

Thanks Aditya!