update cosmos auth to use managed identity

[manvkaur]

This pull request introduces significant updates to the ServerlessLibraryAPI project to enhance authentication flexibility and modernize dependencies. The most important changes include introducing support for DefaultAzureCredential for Cosmos DB authentication, updating NuGet package versions, and suppressing certain build warnings.

Authentication Updates:

• Updated CosmosLibraryStore to support both connection string-based authentication and DefaultAzureCredential for Cosmos DB. This allows the application to use Azure Active Directory for authentication when connection strings are not provided. (ServerlessLibraryAPI/CosmosLibraryStore.cs, ServerlessLibraryAPI/CosmosLibraryStore.csL101-R122)

Dependency Updates:

• Added a reference to the Azure.Identity NuGet package (version 1.5.0) to support DefaultAzureCredential. (ServerlessLibraryAPI/ServerlessLibraryAPI.csproj, ServerlessLibraryAPI/ServerlessLibraryAPI.csprojR14-R27)
• Updated the Microsoft.Azure.Cosmos package from version 3.26.1 to 3.32.0 and the System.Configuration.ConfigurationManager package from version 4.7.0 to 6.0.0 for improved compatibility and feature support. (ServerlessLibraryAPI/ServerlessLibraryAPI.csproj, ServerlessLibraryAPI/ServerlessLibraryAPI.csprojR14-R27)

Build Configuration:

• Added <SuppressTfmSupportBuildWarnings> and set <TreatWarningsAsErrors> to false in the project file to suppress specific build warnings and prevent them from being treated as errors. (ServerlessLibraryAPI/ServerlessLibraryAPI.csproj, ServerlessLibraryAPI/ServerlessLibraryAPI.csprojR14-R27)