[Feature]: Allow system messages + chat messages in palm api

[krrishdholakia]

The Feature

Palm allows this via 'context' and 'messages'. Allow this instead of passing the input in as 'prompt'.

Motivation, pitch

Improve the palm api support.

Twitter / LinkedIn details

No response

[krrishdholakia]

reference: https://developers.generativeai.google/api/rest/generativelanguage/models/generateMessage

[krrishdholakia]

Same for vertex ai

[adi-kmt]

So you want to add here, context and examples are used from the init right?

[SujanShilakar]

@krrishdholakia can you look for my pr for the issue https://github.com/BerriAI/litellm/pull/3718

[SujanShilakar]

@krrishdholakia / @ishaan-jaff fixes for #3718.

• The completion function now supports a structured input with context and messages, making it more aligned with the Palm API's capabilities.
• The PalmConfig class now includes messages as a configurable parameter.
• Configurations are dynamically applied, allowing more flexible and contextually rich responses.
• Ensures that the function constructs the request payload correctly and handles the response appropriately.

request_payload = {
    "context": "This is a test context.",
    "messages": [
        {"author": "user", "content": "User message 1."},
        {"author": "system", "content": "System message 1."},
        {"author": "user", "content": "User message 2."}
    ],
    "temperature": 0.7,
    "candidate_count": 1,
    "top_k": 40,
    "top_p": 0.9,
    "max_output_tokens": 100
}
'''