Include functional tests from cram in coverage reports

[huddlej]

Context

Coverage reports from pytest help us identify large gaps in our tests. Functional tests written in Cram aren't currently reflected in coverage reports, but they likely cover code that isn't covered by unit tests.

Description

Ideally, Cram's coverage could be merged with the pytest coverage prior to uploading to the CodeCov service.

Possible solution

1. Generate coverage from Cram tests by defining a COVERAGE variable prior to Cram execution
2. Run Cram with coverage enabled before pytest in the CI
3. Run pytest with the --cov-append flag so the unit test coverage is added to the functional test coverage