feat: Add CI workflow for linting

Add a Github CI workflow to execute the configured linting checks on
pull requests and when pushing against the main or track/* branches.

Signed-off-by: Phoevos Kalemkeris <phoevos.kalemkeris@canonical.com>

.github/workflows/on_pull_and_push.yaml

@@ -0,0 +1,17 @@
+name: On Pull Request / Push
+
+on:
+  push:
+    branches:
+    - main
+    - track/**
+  pull_request:
+
+jobs:
+  lint:
+    name: Lint
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v3
+      - run: python3 -m pip install tox
+      - run: tox -e lint