Add gitlab CI configuration

.gitlab-ci.yml

+image:
+  name: cp1_testing_image_ex5:latest
+
+stages:
+  - test
+
+default:
+  before_script:
+    - make prepare || /reference/prepare.sh
+
+# Testing the stuff
+#Problem 1
+test_gradient_descent:
+  stage: test
+  tags:
+    - task_check
+  script: make test_gradient_descent
+
+# Problem 2
+test_gradient_root:
+  stage: test
+  tags:
+    - task_check
+  script: make test_gradient_root
+  
+# Problem 3
+test_conjugate_gradient:
+  stage: test
+  tags:
+    - task_check
+  script: make test_conjugate_gradient
+
+# Hidden test cases
+#Problem 1
+test_gradient_descent_hidden:
+  stage: test
+  tags:
+    - task_check
+  script: make test_gradient_descent_hidden
+
+# Problem 2
+test_gradient_root_hidden:
+  stage: test
+  tags:
+    - task_check
+  script: make test_gradient_root_hidden
+  
+# Problem 3
+test_conjugate_gradient:
+  stage: test
+  tags:
+    - task_check
+  script: make test_conjugate_gradient
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