feat: DTOSS-9179 - Transform function completion, and test/logging refactoring

[ianfnelson]

Description

• Completion of FileTransformFunction
• Dependency Injection configuration for NBSS appointment event services (in an extension method within NbssAppointmentEvents namespace).
• Added ValidationErrors field to MeshFile; this maps to an nvarchar(max) in the database.
• Removed FileExtractFunctionConfiguration - this function should use the Mesh Mailbox ID associated with the file that it is processing, not be tied to the NBSS mailbox ID.
• Logging of errors returned by MESH .net client - added an extension method to format these errors (our existing code was logging out the class name!)
• Removed timestamps from information log statements
• Introduce Test Utilities class library; added some static logger assertions to the same
• Refactored function unit tests - introduced helper methods and shared base class to reduce duplication.

Context

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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