Add gitlab-ci using tango image

.gitlab-ci.yml

+image: artefact.skatelescope.org/ska-tango-images/tango-itango:9.3.3.7
+variables:
+  PIP_CACHE_DIR: "$CI_PROJECT_DIR/.cache/pip"
+cache:
+  paths:
+    - .cache/pip
+    - .tox
+before_script:
+  - pip install tox
+stages:
+  - linting
+  - unit-tests
+linting:
+  stage: linting
+  script:
+    - tox -e pep8
+unit_test:
+  stage: unit-tests
+#  image: python:3.6-buster
+  script:
+    - tox -e py36
\ No newline at end of file