- Add the pre-commit hook `trailing-whitespace` to `.pre-commit-config.yaml`
- Apply the hook to all files with the command `pre-commit run -a`

Rationale: building `ASAP::O` from a Docker image on macOS inside a
subdirectory of the source directory can be slow because the files
inside the subdirectory are visible from macOS and macOS does not seem
to handle well when many files changed within a virtual machine. It is
therefore faster to compile from a directory that is not mounted on the
Docker image, which cannot be a subdirectory of the source directory.

Providing the value of `Python_EXECUTABLE` using an environmnet variable
instead of a CMake argument can simplify calls to CMake:

```sh
cmake .. -DENABLE_LIBFABRIC=ON -DCMAKE_BUILD_TYPE="Release" \
  -DBUILD_CLIENTS_ONLY=ON -DBUILD_PYTHON_PACKAGES=source \
  -DNUMPY_VERSION=$NUMPY_VERSION -DPython_EXECUTABLE=python3

export Python_EXECUTABLE=python3
cmake .. -DENABLE_LIBFABRIC=ON -DCMAKE_BUILD_TYPE="Release" \
  -DBUILD_CLIENTS_ONLY=ON -DBUILD_PYTHON_PACKAGES=source \
  -DNUMPY_VERSION=$NUMPY_VERSION
```

This avoids using different Python interpreters for different tasks and
therefore avoid surprises.

Note: CMake files for Windows were not fixed because no Windows
CI runner checks that `ASAP::O` compiles on Windows.

Below is the type of compilation error I was getting:

```
$ cmake -G Ninja ../.. -DPython_EXECUTABLE=python3.7 -DBUILD_TESTS=ON -DENABLE_COVERAGE=ON -DBUILD_CPP_DOCS=ON -DBUILD_PYTHON_DOCS=ON
...
$ ninja
[54/174] Building CXX object producer/api/cpp/CMakeFiles/test-asapo-producer.dir/unittests/test_producer_impl.cpp.o
FAILED: producer/api/cpp/CMakeFiles/test-asapo-producer.dir/unittests/test_producer_impl.cpp.o
ccache /usr/bin/c++  -I/home/marc-olivier/Documents/desy/dev/gitlab.desy.de/asapo/asapo/producer/api/cpp/include -I/home/marc-olivier/Documents/desy/dev/gitlab.desy.de/asapo/asapo/producer/api/cpp/../c/include -I/home/marc-olivier/Documents/desy/dev/gitlab.desy.de/asapo/asapo/common/cpp/include -g -O0 --coverage -fprofile-arcs -ftest-coverage -Wall -Wextra -pedantic -Wconversion -Wno-missing-field-initializers -fPIC -DGTEST_HAS_PTHREAD=1 -std=gnu++11 -MD -MT producer/api/cpp/CMakeFiles/test-asapo-producer.dir/unittests/test_producer_impl.cpp.o -MF producer/api/cpp/CMakeFiles/test-asapo-producer.dir/unittests/test_producer_impl.cpp.o.d -o producer/api/cpp/CMakeFiles/test-asapo-producer.dir/unittests/test_producer_impl.cpp.o -c /home/marc-olivier/Documents/desy/dev/gitlab.desy.de/asapo/asapo/producer/api/cpp/unittests/test_producer_impl.cpp
In file included from /home/marc-olivier/Documents/desy/dev/gitlab.desy.de/asapo/asapo/producer/api/cpp/unittests/test_producer_impl.cpp:15:
/home/marc-olivier/Documents/desy/dev/gitlab.desy.de/asapo/asapo/producer/api/cpp/unittests/mocking.h:20:14: error: ‘uint64_t asapo::MockDiscoveryService::UpdateFrequency()’ marked ‘override’, but does not override
   20 |     uint64_t UpdateFrequency() override {
      |              ^~~~~~~~~~~~~~~
```

As mentioned on
https://stackoverflow.com/questions/729692/why-should-text-files-end-with-a-newline
and
https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_206,
POSIX defines a line as

> A sequence of zero or more non- <newline> characters plus a terminating <newline>
> character.

When a file does not terminate with an empty line, `Git` commands such
as `git diff` show the message `No newline at end of file`.

This commit adds a CI job `pre-commit` to enforce the formatting.

CMake was not generating the files `version.h` and `version_lib.go` into
the project source directory when building from a subdirectory such as
`./build/debug/`. So these files could not be found during compilation.