chore(yamllint): add and integrate yamllint

.gitlab-ci.yml

 image: python
 
 stages:
+  - lint
   - tests
   - after-tests
 
@@ -108,5 +109,16 @@ trigger-readthedocs:
       - branch/default
   stage: after-tests
   script:
-  # regarding the " everywhere when there is a '%': yaml is extremly weird when % are involved
-  - curl -X POST -d "token=${READTHEDOCS_TOKEN}" https://readthedocs.org/api/v2/webhook/logilab-common/89595/ -w "\nhttp code:"\ "%{http_code}\n" -f
+    # regarding the " everywhere when there is a '%': yaml is extremly weird when % are involved
+    - curl -X POST -d "token=${READTHEDOCS_TOKEN}" https://readthedocs.org/api/v2/webhook/logilab-common/89595/ -w "\nhttp code:"\ "%{http_code}\n" -f
+
+yamllint:
+  stage: lint
+  rules:
+    - changes:
+        - "**/*.yaml"
+        - "*.yaml"
+        - "**/*.yml"
+        - "*.yml"
+  script:
+    - tox -e yamllint

.yamllint

+extends: default
+
+rules:
+  document-start: disable
+  line-length: disable
+  indentation:
+    spaces: 2

MANIFEST.in

@@ -18,3 +18,4 @@ prune debian
 prune docs/_build
 exclude .hgrc
 exclude .gitlab-ci.yml
+exclude .yamllint

tox.ini

 [tox]
-envlist=py3,check-manifest,mypy,flake8,black,black-run
+envlist=py3,check-manifest,mypy,flake8,black,black-run,yamllint
 
 [testenv]
 deps =
@@ -94,3 +94,9 @@ commands =
   dpkg-buildpackage -us -uc --no-check-builddeps --build=source "
   sh -c "cd dist && dcmd zip latest.zip *.changes"
   http -f POST https://{env:JENKINS_USER}:{env:JENKINS_TOKEN}@jenkins.intra.logilab.fr/job/pkg-from-dsc/buildWithParameters DIST=buster source.zip@dist/latest.zip REPO=buster PUBLISH=true
+
+[testenv:yamllint]
+skip_install = true
+deps = yamllint
+commands =
+  yamllint .