Add pybind11 as a build dependency

[chapulina]

The 6.9.3~pre1 pre-release failed. I think the first step is to add pybind11 as a dependency, but there may be other issues. @j-rivero , is it ok to add a build dependency to a stable version?

Test build:

[j-rivero]

The 6.9.3~pre1 pre-release failed. I think the first step is to add pybind11 as a dependency, but there may be other issues. @j-rivero , is it ok to add a build dependency to a stable version?

I would not recommend to do it since it potentially affect downstream packaging work in distributions if the dependency is not available on them. In this case, if we threat as an optional dep, the worst case would be the lack of python bindings in the package which is not nice but probably packagers can deal with it. Speaking about Debian I don't remember anything in the policy against adding new dependencies if they are available and ABI/API stability is guarantee.

[chapulina]

Thanks for the feedback, I think I moved it to the right place in a423f03?

The build is still failing though, I opened gazebosim/gz-math#360 to help debug it

[chapulina]

I think I moved it to the right place in a423f03?

Now while testing #9 I think I didn't. We need pybind11 to be available during build time. So I'll move it back to be a build dependency.

if we threat as an optional dep, the worst case would be the lack of python bindings in the package which is not nice but probably packagers can deal with it.

This will be the situation.