In #2813 we introduced a command that allows you to operate on an AAD app using information stored in a .m365rc.json file, which contains the appId property with the ID of the AAD app. We should extend the aad app app command with a new --save option. When used, it will cause the command to write the information about the newly created app to the .m365rc.json file in the working directory.

The logic for writing to the file:

• check if the file exists, create if it doesn't
• read the file contents as JSON, if there's an exception, throw
• if the read object has the appId property, update its value. If it doesn't, set it
• write the updated object back to the file