ci: enable codecov on repo

[andrewb1269]

Enable codecov on this repo as mentioned in audit story #20

[andrewb1269]

Some notes:
This is the solo example:
https://github.com/hashgraph/solo/blob/main/codecov.yml
https://github.com/hashgraph/solo/blob/main/.github/workflows/zxc-code-analysis.yaml one workflow

Though codecov.io will probably give you cleaner examples of both

[andrewb1269]

- name: Upload test results to Codecov
  if: ${{ !cancelled() }}
  uses: codecov/test-results-action@v1
  with:
    token: ${{ secrets.CODECOV_TOKEN }}