Copilot Chat Tasks - Rename CopilotChatApi to CopilotChatWebApi

[lemillermicrosoft]

This commit renames the CopilotChatApi project and related files to CopilotChatWebApi, to avoid confusion with the CopilotChatApp project and to follow the naming convention of other webapi projects in the solution. It also updates the launch and task configurations in VSCode to reflect the new name.

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: