Add back CI job to perform automatically clang-format on code

We removed the CI job performing the application of the clang-format as it started failing. The yml script was based upon the Rec one: https://gitlab.cern.ch/lhcb/Rec/blob/master/.gitlab-ci.yml .

Some pointers for whoever looks into this:

• Line 24 of that script should be changed to fetching our clang-format (that is different from the one online). Concretely this line:

    -   curl -o .clang-format "https://gitlab.cern.ch/lhcb-core/LbDevTools/raw/master/LbDevTools/data/default.clang-format?inline=false"

• It could be that some of the options in our clang-format are not supported in whatever version gitlab-registry.cern.ch/lhcb-docker/style-checker ships of clang-format. It's unclear why did it start failing.