Continuing #8690.
Given that `Centipede` passed CI tests of the 5 projects in #8690, we
will gradually roll it out to let more real-world fuzzing targets
benefit from it.
The second round contains the following 5 projects, **some of which are
not from Google** (unlike round 1):
1. `skcms`,
2. `abseil-cpp`,
3. `alembic`,
4. `arduinojson`,
5. `aspell`.
Projects are selected because:
1. They are `C++` projects.
There will be another round (of 10 projects) as soon as we can confirm
that Centipede works fine in this round.
* [presubmit] Enforce language attribute in projectt.yaml to be always set.
* Update documentation, better presubmit check, new project template.
* add docstring to templates.py
* Add example values in the project.yaml template and remove python value for now
* Add "project: c++" to 256 projects
* format
* Add labels and selective_unpack sections to the presubmit check
* fix incorrect auto_ccs format in three projects
* fix nss emails after rebase
Dongge Liu