[1.17] Add Conversation API new fields #1639

Update the Conversation (Alpha2) client to support the latest API surface so it matches the Conversation API reference.

For the request add:

• responseFormat – Optional. Structured output via a JSON Schema object
• promptCacheRetention – Optional. Prompt cache retention.

For the response add:

• model – Optional. Model identifier used for the completion.
• usage – Optional. Token usage

Reference:

• Proto/API definitions: Check the ai.proto file changes in this PR https://github.com/dapr/dapr/pull/9316/changes#diff-cc02342970a5222eef2c5aee936883611b8457feb8d3afd80763c3ebd93e3c5e
• Docs PR: docs(convo): add new fields and make corrections on caching docs#5027
• Go SDK: feat(convo): add new fields to conversation api go-sdk#801
• Python SDK: feat(convo): add new fields to conversation api python-sdk#902