Add Bazel support

[bcebere]

Feature Description

Bazel support would have numerous advantages in TenSEAL's build system.

Pros

• We would be extending the cmake build system, not replacing it.
• Well-established ML tools like PyTorch or Tensorflow support Bazel too, and it would make the integration seamless there.
• The integration with SEAL would be easy, no submodule required, as in this example. Bazel has bindings to other build systems as well https://github.com/OpenMined/PIR/blob/master/third_party/seal.BUILD
• It would be a major improvement for integration/deployment in Bazel system, it would install all the depends without any hassle, just the TenSEAL reference in their bazel file, as in this example https://github.com/OpenMined/PIR
• It supports multiple languages, like C++/Python/Go/Rust and so on.
• It supports pytest/gtest, no need for installing/running extra tools. Just bazel test and it executes all the tests in the repository, no matter the language/framework.

Cons

• pip support exists, but I am not sure it works fine with pybind, I wasn't able to make it work in this example https://github.com/OpenMined/PSI/blob/py-setuptools/setup.py
• Bazel can be unstable, the API might change between updates.

[bcebere]

I'll work on this one.