cov : add Code Coverage and codecov.io integration (#2928)
* update .gitignore
* makefile: add coverage support (lcov, gcovr)
* add code-coverage workflow
* update code coverage workflow
* wun on ubuntu 20.04
* use gcc-8
* check why the job hang
* add env vars
* add LLAMA_CODE_COVERAGE=1 again
* - add CODECOV_TOKEN
- add missing make lcov-report
* install lcov
* update make file -pb flag
* remove unused GGML_NITER from workflows
* wrap coverage output files in COV_TARGETS
