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

Please, prepare your MR for a review. Be sure to write a summary and a focus and create gitlab comments for the reviewer. They should guide the reviewer through the changes, explain your changes and also point out open questions. For further good practices have a look at our review guidelines

• 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.

.gitlab-ci.yml

@@ -81,6 +81,17 @@ code_style:
     - clang-format-11 --dry-run --verbose --Werror $(find test/ src/ include/ -type f -iname "*.cpp" -o -iname "*.h" -o -iname "*.h.in")
   allow_failure: true
 
+
+# build with vcpkg
+build_vcpkg:
+  tags: [ docker ]
+  stage: test
+  script:
+    - apt update && apt install -y pkg-config 
+    - cd vcpkg && git fetch origin 5d3798ac7388ca66c169773e46103b14077b76a4 && cd ..
+    - make vcpkg-build-release
+  allow_failure: true
+
 # unit tests with gtest
 test:
   tags: [ docker ]