added codeowners file as part of Issue UNICADO/Unicado-Package #6

See UNICADO/Unicado-Package#6

CODEOWNERS

+# Repository-specific code ownership
+  *                           @unicado-consortium/tum   @unicado-consortium/tuhh    @unicado-consortium/tub-fmra
+
+# File-specific code ownership
+.gitattributes                @Florian.Schueltke
+.gitignore                    @Florian.Schueltke
+.gitlab-ci.yml                @maurice.zimmnau   @kristina.mazur
+CMakeLists.txt                @Florian.Schueltke
+CMakePresets.json             @Florian.Schueltke
+CODEOWNERS                    @Florian.Schueltke
+LICENSE                       @Florian.Schueltke
+README.md                     @Florian.Schueltke