Add Jacoco and uploads test results to codecov

[marandaneto]

See Java repo https://app.codecov.io/gh/getsentry/sentry-java

[cortinico]

when doing this, we can remove the Upload Test Results step from pre-merge.yaml

The reason behind that step is to be able to easily see what was the failure in the tests. I'm not sure uploading code coverage to codecov will include also test results (like stacktraces and so on).

[marandaneto]

yeah they are not really related, my bad, this issue is more about the codecov