feat(datahub-client): improve Avro schema conversions

[sgomezvillamor]

Improvements:

• Map types become a nested type with a value field. No support yet for key; assumed/required string type.
• Array types become a nested type with items field.
• Collapse nullability unions: Avro unions for nullability become the actual type with nullable indicator instead of the raw union.

To do:

• Improve UI
• Python-Java compatibility

Context:

• This is fixing the concerns raised when adding tests in another PR tests(datahub-client): new tests for the AvroSchemaConverter #12087

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

see 181 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f9251c8...42aff3b. Read the comment docs.