Merge main into next/core

[rido-min]

This pull request introduces significant improvements to cloud environment support and authentication flexibility in the Teams API SDK, while also cleaning up legacy and experimental features. The main focus is on enabling multi-cloud support (including USGov, DoD, and China) through a new CloudEnvironment abstraction, updating authentication flows to use cloud-specific endpoints, and ensuring that token and service URLs are configurable and propagated across client instances. Additionally, the pipeline configuration is modernized and consolidated.

Cloud Environment & Authentication Enhancements

• Introduced the CloudEnvironment class in Microsoft.Teams.Api.Auth, encapsulating all cloud-specific endpoints, scopes, and service URLs, with predefined instances for Public, USGov, USGovDoD, and China clouds, and support for custom environments. (Libraries/Microsoft.Teams.Api/Auth/CloudEnvironment.cs)
• Updated ClientCredentials to accept and use a CloudEnvironment property, ensuring that all authentication requests (token endpoints, tenants, etc.) are cloud-aware and configurable. (Libraries/Microsoft.Teams.Api/Auth/ClientCredentials.cs) [1] [2]

Client Propagation of Cloud Settings

• Modified ApiClient and related sub-clients to propagate cloud-specific token service URLs and scopes, ensuring consistent behavior when cloning or instantiating new clients with different cancellation tokens. (Libraries/Microsoft.Teams.Api/Clients/ApiClient.cs)
• Updated BotSignInClient to use a configurable TokenServiceUrl property instead of a hardcoded URL, and applied this property in all relevant API calls. (Libraries/Microsoft.Teams.Api/Clients/BotSignInClient.cs) [1] [2] [3]

Pipeline Modernization

• Migrated and consolidated the NuGet publishing pipeline to use the 1ES Official Pipeline Template, supporting both internal and public publishing, with improved security compliance and parameterization. (.azdo/publish.yaml, .azdo/publish.yml) [1] [2]

Legacy/Experimental Cleanup

• Removed the experimental IsTargeted property and related logic from the Activity class, simplifying the activity model and removing obsolete code paths. (Libraries/Microsoft.Teams.Api/Activities/Activity.cs) [1] [2] [3]

[rajan-chari]

Got it merge from main.