Add separate target for unit tests for easier test access. Remove unit tests from ResInsight application. (#11184)

Clean up cmake configuration a bit, and pull down gtest when needed, no longer use a thirdparty subfolder
Add a ResInsight-tests target to run the unit tests

.github/workflows/ResInsightWithCache.yml

@@ -240,11 +240,12 @@ jobs:
 
       - name: Stats for buildcache
         run: ${{ github.workspace }}/buildcache/bin/buildcache -s
+
       - name: Run Unit Tests
         if: matrix.config.execute-unit-tests
         shell: bash
         run: |
-          cmakebuild/ApplicationExeCode/ResInsight --unittest
+          cmakebuild/ApplicationLibCode/UnitTests/ResInsight-tests
 
       - name: (Python) Check types using mypy
         if: matrix.config.build-python-module