fix: Updated readme for role assignment and file name

[Ragini-Microsoft]

This pull request updates documentation files to reflect changes in role naming conventions and backend application execution commands. The most important changes include updates to Azure role assignments and adjustments to the commands for running the backend application.

Updates to Azure role assignments:

• docs/DeploymentGuide.md: Changed the role name from "Cognitive Services OpenAI User" to "Azure AI User" in the Azure CLI command for role assignment.
• docs/LocalDeployment.md: Updated the role name in the Azure CLI command for role assignment to match the new naming convention.

Updates to backend application execution commands:

• docs/DeploymentGuide.md: Modified the command to run the backend application from python app.py to python app_kernel.py.
• docs/LocalDeployment.md: Adjusted the backend application execution command to use python app_kernel.py instead of python app.py.## Purpose

• ...

Does this introduce a breaking change?

• Yes
• No

How to Test

• Get the code

git clone [repo-address]
cd [repo-name]
git checkout [branch-name]
npm install

• Test the code

What to Check

Verify that the following are valid

• ...

Other Information