Include code coverage in continuous integration

[rikurauhala]

Code coverage has been set up for our end-to-end tests. However, the report is not very useful if it can only be generated locally which takes a lot of time and maintains no history of the progress.

The coverage should be calculated and a report for it generated with GitHub Actions. The report should be pushed to Codecov.

Also pushing the coverage to Code Climate would be a nice addition but the actual UI/UX is much worse than with Codecov.

There is probably no need to include the coverage report in our current workflows. There could be a new separate workflow that runs at regular intervals, say once a day or once a week.

Steps to generate the report:

• Instrument the code: npm run instrument
• Run Oodikone with the instrumented code: npm run oodikone:test
• Run tests in the terminal: npm run cypress run -- --browser chrome
• View the report: firefox coverage/lcov-report/index.html

UPDATE: This has probably changed after the introduction of TypeScript to Oodikone.