Move authority out from Constants.ts to the .env (env.example)

[craigomatic]

Motivation and Context

Small PR to shift the AAD authority out of the Constants.ts file to the .env alongside the AAD client id. Developers may wish to change the authority from /common to the MSA endpoint /9188040d-6c67-4c5b-b112-36a304b66dad if their AAD app is for consumer MSA logins or to their own tenant for other reasons.

Description

Change only the location of the default authority to the env.example file. The expectation is that the developer will rename the env.example file to .env

Contribution Checklist

• [x] The code builds clean without any errors or warnings
• [x] The PR follows SK Contribution Guidelines (https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
• [x] The code follows the .NET coding conventions (https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions) verified with dotnet format
• [x] All unit tests pass, and I have added new tests where possible
• [x] I didn't break anyone :smile: