Updated documentation for ASP.NET Identity Community Providers

[toiyabe]

Updated Documentation for Community Supported Cosmos DB Store Providers

• [X ] You've read the Contributor Guide and Code of Conduct.
• [X ] You've included unit or integration tests for your change, where applicable.
• [X ] You've included inline docs for your change, where applicable.
• [ X] There's an open issue for the PR that you are making. If you'd like to propose a new feature or change, please open an issue to discuss the change or find an existing issue.

Summary of the changes (Less than 80 chars)

Description

Added a section in documentation for community supported Cosmos DB store providers for ASP.NET Core Identity.

[ghost]

Thanks for your PR, @toiyabe. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.