[Maintenance] Improve unit test coverage reporting

[illiakovalenko]

Description / Motivation

Introduce Cobertura - code coverage reporter which compatible with many testing libraries and with azure pipelines.

• reportgenerator extension is installed to generate a fancy and user friendly html report
• PublishCodeCoverageResults publish generated html report to azure pipelines

Testing Details

Types of changes

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

[ambrauer]

Looks good! Approved with some comments. Would be nice to group the report by package as it is difficult to determine where source file originates, but this looks to be a limitation of Cobertura.