Doxygen doc generation

Add a Doxyfile in the doc folder to generate some documentation. The only source folder included in the documentation is src/shared with the exclusion of src/shared/utils/testutils because I think is not relevant since contains the Catch file for the UT.

The CI pipeline has been also updated to generate and publish automatically the documentation here https://documentation.skywarder.eu/

As possible future extension we could limit the documentation generation only to a subset of branches.