Updated conversation api docs to latest alpha v2 with tool calling

[bibryam]

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Description

Updated Conversation API docs to v1.0-alpha2 with tool calling
-Aligned documented fields with the code: metadata, tool_choice, temperature,

• Clarified URL/body/YAML precedence for metadata
• Refreshed request/response examples with real curl commands and consistent JSON format, ready to use
• Converted message types into a table for easier reference (aligned with tool calling format).
• Removed redundant fields (e.g. name, camelCase variants) and standardized on snake_case (as per code)

Issue reference

#4687

[marcduiker]

Can the prompt caching be described in a bit more detail? See the comment.

[marcduiker]

LGTM

[bibryam]

reverted back to camel case