Schema Registry support: delete_version does not support the "permanent" flag

[xdgrulez]

Description

In the REST API, the Schema Registry supports "permanent=True" (hard delete) not only on subjects, but also on versions. This is missing in confluent_kafka.

How to reproduce

Just compare the spec of

delete_version(subject_name, version)

with the REST API spec:

https://docs.confluent.io/platform/current/schema-registry/develop/api.html#delete--subjects-(string-%20subject)-versions-(versionId-%20version)

Checklist

Please provide the following information:

• [X ] confluent-kafka-python and librdkafka version (confluent_kafka.version() and confluent_kafka.libversion()): latest (2.6.0)
• Apache Kafka broker version: not relevant for this issue
• Client configuration: {...} not relevant for this issue
• Operating system: not relevant for this issue
• Provide client logs (with 'debug': '..' as necessary) not relevant for this issue
• Provide broker log excerpts not relevant for this issue
• Critical issue

[allamiro]

Ensure alignment with the official Schema Registry API documentation:

• Add examples for the permanent flag in the library's usage guide.
• Provide a clear distinction between soft and hard delete behavior.

[rayokota]

Fixed by #1867