Create `library` for Unit Testing

[sokimaaa]

Context

• JUnit and Mockito have a lot of dependencies that takes a lot of place and makes messy dependencies block in pom.xml
• Let's create only one library that has itself all of these dependencies to simply inject only one
• In future general purpose utils for unit testing are going to be placed here

Acceptance Criteria

• Created library structure
• Added all often-used testing dependency
• Consider using JUnit 5.9.X+
• Consider using Mockito 5.2.X+
• Registered library in 6core-BOM
• Added unit testing library to all app/domain modules

Technical Details

• Explore what dependencies are needed for Unit Testing
• Explore dependency for ParametrizedTest, MockitoExtends, some other useful things

[andrey-kiyas]

Link to pull request for the current task