Bugfix/2854 fix validate code

[mmsmits]

This pull request includes several changes to the Hl7.Fhir.Base library, focusing on enhancing the ValidateCodeParameters class and associated functionality. The most important changes include adding a new attribute inferSystem, modifying validation logic, and updating relevant tests.

Enhancements to ValidateCodeParameters:

• Added a new private constant URLATTRIBUTE in ParametersExtensions.cs to support URL-based validation.
• Introduced a new attribute inferSystem in the ValidateCodeParameters class, along with corresponding getter and setter methods. [1] [2] [3]
• Updated the WithCode method in ValidateCodeParameters.cs to include the inferSystem parameter.

Validation logic updates:

• Changed the validation logic in CheckForValidityOfValidateCodeParams to require a URL or context instead of a system or context.
• Updated error messages in LanguageTerminologyServiceTests.cs and MimeTypeTerminologyServiceTests.cs to reflect the new validation logic. [1] [2]

Test updates:

• Added new tests in TerminologyTests.cs to verify the functionality of ValidateCodeParameters with the new inferSystem attribute and URL-based validation.

[ewoutkramer]

This fixes #2854.