Add CI for backend opencv

Add .gitlab files for CI. CI depends on MR dataloader aidge/aidge_core!4 to pass.

.gitlab/ci/_global.gitlab-ci.yml

+################################################################################
+# Centralized definitions of common job parameter values.                      #
+# Parameters with many optional configurations may be in separate files.       #
+#                                                                              #
+################################################################################
+variables:
+  GIT_SUBMODULE_STRATEGY: recursive
+  OMP_NUM_THREADS: 4
+  GIT_SSL_NO_VERIFY: 1
+  DEBIAN_FRONTEND: noninteractive
+
+# See https://docs.gitlab.com/ee/ci/yaml/workflow.html#switch-between-branch-pipelines-and-merge-request-pipelines
+workflow:
+  rules:
+    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
+    - if: $CI_COMMIT_BRANCH && $CI_OPEN_MERGE_REQUESTS
+      when: never
+    - if: $CI_COMMIT_BRANCH
+
+default:
+  image: nvidia/cuda:12.2.0-devel-ubuntu22.04
+  before_script:
+    - apt update
+    - apt install -y cmake cppcheck python-is-python3 pip git gcovr unzip curl libopencv-dev