Fix deprecations + updates

See merge request !57

See !92 for the relevant issue.

Resolve "Unit tests unter Windows"

See merge request !56

- Fix GTest spelling in test/CMakeLists.txt
- Restrict vcpkg triplet to release
- Add set(CMAKE_POSITION_INDEPENDENT_CODE ON)
- Include of <gtest/gtest.h> in tests instead of smaller headers
- Add boost options to CMakeLists.txt

This should be done by the Docker image

For activating the conan venv in ~/.bashrc

- Add test targets for both Debug and Release

boost::filesystem::load_string_file was removed in boost 1.84

See https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0174r2.html#2.1

- add scopes to enforce destruction of FileWriter, i.e. close file
- only check file size after writing the complete file

Something something string literals on Windows...

The singleton instances of ConfigurationManager and ConnectionManager
were stored as static variables in the static GetInstance methods.

This causes weird errors on Windows where the singleton instance is not
initialized in time and remains empty. This could be due to
undefined behavior?

Moving them to the namespace level fixes the unit test errors.

Resolve "Windows: Linker errors with protobuf-generated code"

See merge request !54

Rename caosdb-cpplib to linkahead-cpplib

See merge request !55