Fix selection of custom ContextManager through CslaOptions

[rockfordlhotka]

Fixes #4047

This pull request addresses the issue of ApplicationContextAccessor not selecting the ContextManager specified in CslaOptions.ContextManagerType over the default one. The changes ensure that custom ContextManager types are prioritized and registered before the default types, allowing for the correct ContextManager to be used according to the configuration.

• Modifies the RegisterContextManager method in ConfigurationExtensions.cs to use TryAddScoped instead of AddScoped for registering default ContextManager types. This change prevents overwriting custom registrations if a custom ContextManagerType is provided in CslaOptions.
• Ensures that if a custom ContextManagerType is specified, it is registered before attempting to register any default ContextManager types, allowing the custom type to take precedence.
• Applies TryAddScoped in the LoadContextManager method for loading specific ContextManager types based on the environment, further ensuring that custom types are not overwritten by default or environment-specific types.

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[rockfordlhotka]

This isn't complete. It is my first attempt at using the new GH Copilot workspace preview feature. Not entirely sure the AI did the right thing, and in any case, it didn't generate (or allow me to add) any unit tests.