Combine build file of adolc and tests; Add code coverage

[TimSiebert1]

Hi,
this PR includes:

1. an updated CMakelists.txt that includes a new CMAKE_BUILD_TYPE called Tests and TestsWithCov. If Tests is specified cmake builds the boost-test-adolc (in build dir) without the need of specifying the adolc paths. In addition enables the use of ctest. If TestsWithCov is specified, adolc and boost-test-adolc are compiled with coverage related flags. These flags are required in a corresponding coverage workflow

2. an adapted workflow tests.yml which now leverages ctest

3. a workflow coverage.yml for generating a coverage report with lcov and codecov. This is mainly useful if we could add a github-secret for this repository. @awalther1 should be able to do it. If the token is set, the coverage report is posted on a page that would look like this: https://app.codecov.io/gh/TimSiebert1/ADOL-C.

I will update the README.md files for building the test once everything is working well

[codecov]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

Thanks for integrating Codecov - We've got you covered ☂️

[TimSiebert1]

Oh there seems to be a code_cov token already. Nice! Once this is merged we will find the coverage report here: https://app.codecov.io/github/coin-or/ADOL-C.