Read dotnet.config file to use MTP or VSTest in dotnet test

[mariam-abdulla]

This pull request includes significant changes to the TestCommandParser class in the dotnet-test command. The primary focus of these changes is to improve the configuration handling and test runner determination logic.

Configuration handling improvements:

• src/Cli/dotnet/commands/dotnet-test/TestCommandParser.cs: Added Microsoft.Extensions.Configuration to handle configuration files.
• src/Cli/dotnet/commands/dotnet-test/TestCommandParser.cs: Introduced the GetTestRunnerName method to determine the test runner based on the dotnet.config file.

Test runner determination logic:

• src/Cli/dotnet/commands/dotnet-test/TestCommandParser.cs: Replaced the IsTestingPlatformEnabled method with GetTestRunnerName to dynamically determine the test runner name from the configuration file.
• src/Cli/dotnet/commands/dotnet-test/TestCommandParser.cs: Updated the ConstructCommand method to use the new GetTestRunnerName method for selecting the appropriate CLI command.
• src/Cli/dotnet/commands/dotnet-test/TestCommandParser.cs: Added the GetDotnetConfigPath helper method to locate the dotnet.config file starting from the current directory.

Relates to #45927

[KalleOlaviNiemitalo]

Was there a decision to call the INI file dotnet.config? *.config files used with System.Configuration have XML format, so if you're going to use INI format here, then I'd prefer naming the file dotnet.ini or dotnet-config.ini.

[Evangelink]

The file name and format are still under discussion but as we need to move forward to allow internal dogfooding it was decided to temporarly move on with that (cc @baronfel )

[KalleOlaviNiemitalo]

On Windows, should this disallow reading dotnet.config from the root directory of a volume, like #33216 and #33282 disallow reading .config\dotnet-tools.json from there?

[KalleOlaviNiemitalo]

I suppose such a restriction is not necessary for security because the volume root directory on Windows typically has an NT AUTHORITY\Authenticated Users:(AD) access control entry. This ACE allows the user to create a subdirectory such as .config in the root directory, and the user can then get full control on the new subdirectory and create a dotnet-tools.json file in there. However, the ACE does not allow the user to create a file such as dotnet.config or global.json directly in the root directory. See FILE_ADD_SUBDIRECTORY in File Access Rights Constants.