Code coverage plugin

[Tlacenka]

As a Code PushUp user, I want to be able to see my code coverage results in the Code PushUp report.

Acceptance criteria

• Code coverage plugin is implemented.
• The plugin has sufficient documentation of its interface and usage.
• The plugin is covered by tests.
• Its audits as well as issues can be checked in portal.
• Preset for unit tests is added to our code-pushup.config.ts for dogfooding.
• Integration tests are added to our code-pushup.config.ts via nx helper for dogfooding.
• The plugin is published and referenced in our README.
• The plugin is fully integrated to all CLI commands (project.json)

Implementation details

• One can choose whether to only provide code coverage results or run a specified command first to collect results.
• Paths to coverage results are provided either as an array (simple project) or deduced via nx helpers (uncovering path to project within workspace).
• E2E should be implemented to test running a coverage command tool on our example repo.
• Both integration and unit test results are used for dogfooding.
• Audits are provided as a group for convenience.
• A unified format is chosen for the expected results (currently between XML cobertura and LCOV).
• Audit is a type of coverage (function, branch, condition, statement/line) for the whole project.
• Issue is a finding of missing coverage (table can be filtered by folder for issues within one package).

Additional post-MVP features

#498

Detailed research available on demand.