adding ssh support for git clone

.gitlab-ci.yml

+build:
+  stage: build
+  tags:
+    - docker-builder
+  image: docker:latest
+  variables:
+    DOCKER_BUILDKIT: 1
+    GIT_SUBMODULE_STRATEGY: recursive
+    GIT_SUBMODULE_DEPTH: 1
+    GIT_SUBMODULE_UPDATE_FLAGS: --jobs 4
+  before_script:
+    - docker info
+    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
+  script:
+    - docker build --pull --file Dockerfile --tag $CI_REGISTRY_IMAGE:latest  .
+    - docker push $CI_REGISTRY_IMAGE:latest

Dockerfile

+FROM ubuntu:22.04
+
+# ================================================================================
+# Linux applications and libraries
+# ================================================================================
+
+RUN apt update --yes \
+ && apt install --yes --quiet --no-install-recommends \
+    openssh-client \
+ && apt clean \
+ && rm -rf /var/lib/apt/lists/*
+