Add a managed app deployment as an option

[jgbradley1]

This PR adds instructions and code changes to support the conversion of the existing deployment to an Azure Managed App for an improved deployment experience.

Manual deployments using the existing deployment guide and shell script (infra/deploy.sh) will always be supported as we seek to improve the deployment experience inside Azure.

[jgbradley1]

Some additional changes included in this PR are

• updated dependencies of the graphrag backend docker image
• reverted the graphrag backend docker image to use a FastAPI app instead of using fastapi-offline. This was done to make the swagger docs page user friendly (users can now use the Try it out feature inside the swagger doc page to make REST calls. The attempt to use fastapi-offline led to other problems with APIM blocking the requests to the downloaded FastAPI static css files (making the entire swagger doc page unusable).
• Reduced the number of deployment variables a user must define down to 2.
• Reset the helm chart version=0.0.1 and defined appVersion=1.2.0. For future reference, we will start following the rule that appVersion will be a 1:1 mapping to the version of the graphrag library that is used in the accelerator for better clarity.