DGS-22077 Handle evolution during field transformation

[rayokota]

What

• Handle evolution during field transformation
• Also change Accept-Version to Confluent-Accept-Unknown-Properties

Checklist

• [Y] Contains customer facing changes? Including API/behavior changes
• [Y] Did you add sufficient unit test and/or integration test coverage for this PR?
  • If not, please explain why it is not required

References

JIRA:

Test & Review

Open questions / Follow-ups

[Copilot]

Pull Request Overview

This PR handles schema evolution during field transformation by ensuring that field transformations use the original schema definition rather than an evolved schema. The key change enables proper transformation when fields are added or removed between schema versions.

• Modifies REST service to accept unknown properties during schema evolution
• Updates field transformation logic to reference original field schemas
• Adds test coverage for field transformation with missing properties

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
test/Confluent.SchemaRegistry.Serdes.UnitTests/SerializeDeserialize.cs	Adds test case for field transformation with missing properties to verify evolution handling
src/Confluent.SchemaRegistry/Rest/RestService.cs	Replaces version header with unknown properties acceptance header
src/Confluent.SchemaRegistry.Serdes.Avro/AvroUtils.cs	Updates transformation logic to use original field schemas and handle evolved records

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[sonarqube-confluent]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube