fix: rate limit error message change

[Ravikirana-Microsoft]

Purpose

This pull request makes updates to the src/backend/app_kernel.py file, focusing on improving error messaging and adding clarity to middleware configuration. The most significant changes include refining error messages for rate limit scenarios, simplifying exception details, and clarifying a comment in the CORS middleware setup.

Error messaging improvements:

• Updated the error message for rate limit scenarios to a more user-friendly and generic message: "Application temporarily unavailable due to quota limits. Please try again later." ([src/backend/app_kernel.pyL272-R272](https://github.com/microsoft/Multi-Agent-Custom-Automation-Engine-Solution-Accelerator/pull/356/files#diff-c839d97b372f2799977f9f197d6c18667f795b2566b1b2c42e27b1479be26173L272-R272))
• Simplified the HTTPException detail message by removing redundant text and directly using the error_msg variable. ([src/backend/app_kernel.pyL282-R282](https://github.com/microsoft/Multi-Agent-Custom-Automation-Engine-Solution-Accelerator/pull/356/files#diff-c839d97b372f2799977f9f197d6c18667f795b2566b1b2c42e27b1479be26173L282-R282))

Middleware configuration:

• Added a clarifying comment to the allow_origins parameter in the CORS middleware, specifying that all origins are allowed for development but should be restricted in production. ([src/backend/app_kernel.pyL77-R77](https://github.com/microsoft/Multi-Agent-Custom-Automation-Engine-Solution-Accelerator/pull/356/files#diff-c839d97b372f2799977f9f197d6c18667f795b2566b1b2c42e27b1479be26173L77-R77))

Does this introduce a breaking change?

• Yes
• No

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Other Information

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