feelpp Use FindPkgConfig and petsc.pc instead of FindPETSc.cmake closes #1913

[x] Have you checked to ensure there aren't other open Pull Requests for the same change?
[x] Have you added an explanation of what your changes do and why you'd like us to include them?
[ ] Have you written new tests for your changes?
[ ] Have you successfully run the Feel++ testsuite with your changes locally?
[x] Have you written Doxygen comments in your contribution ?

closes #1913
closes #1914

Sep 09 '22 21:09 prudhomm

to do still

[ ] #1914

Sep 11 '22 07:09 prudhomm

@vincentchabannes feel++ compiles on fedora:37 (I haven't tested yet on fedora:36), several compilation fixes have been made due to clang 14. Also the documentation of the toolbox applications have been updated and are now generated automatically

Oct 23 '22 21:10 prudhomm

@vincentchabannes the PR builds fine. The remaining builds are due to changes to build fedora via github actions. The important build is this one: https://buildkite.com/feelpp/feelpp/builds/4655. Please review

Oct 24 '22 10:10 prudhomm

the current build is here : https://buildkite.com/feelpp/feelpp/builds/4668

Oct 31 '22 12:10 prudhomm