Add vcpkg support

Summary

While exploring vcpkg I realized that with Conan 2 it should be possible to actually offer both Conan and vcpkg as package managers. This MR brings support for compilation with vcpkg to the cpplib.

Related to #81 (closed)

Focus

• A few files were added to support vcpkg, and some changes had to be made to the CMakeLists.txt file to make it compatible with both Conan 2 and vcpkg.
• Instructions on how to build with vcpkg can be found in docs/Install_develop.rst.
• A GitLab CI step to test building with vcpkg was added to the pipeline.

Test Environment

Follow new build instructions to test vcpkg.

Check List for the Author

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• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Up-to-date JSON schema (or not necessary)
• Appropriate user and developer documentation (or not necessary)
  • How do I use the software? Assume "stupid" users.
  • How do I develop or debug the software? Assume novice developers.
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.