Added config watcher (#1)

Added Kubernetes configuration watcher. It uses the Kubernetes API to watch for
changes on ConfigMap or Secret resources and create files in the target
directory corresponding to the resource's `data` field. Multiple Kubernetes 
namespaces can be watched for changes. An optional webhook URL is invoked
when a change in resource results in a file content change in the target directory.
There are no guards for duplicate keys in ConfigMap resources.

Added `Dockerfile` and GitHub Actions to run the available tests.

Author: sivanov-nuodb

.dockerignore

@@ -0,0 +1,6 @@
+# More info: https://docs.docker.com/engine/reference/builder/#dockerignore-file
+# Ignore build and test binaries.
+
+# top-level directories to ignore
+bin/
+tmp/

.github/workflows/test.yaml

@@ -0,0 +1,59 @@
+name: Test
+
+on:
+  pull_request:
+  push:
+    branches:
+      - "main"
+
+jobs:
+  continuous:
+    name: Continuous
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.12"]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+          cache: 'pip'
+      - name: Install dependencies
+        run: |
+          pip install -r config_watcher/test-requirements.txt
+          pip install -r config_watcher/requirements.txt
+      - name: Test code formatting
+        run: |
+          make fmt
+          status="$(git status --porcelain)"
+          if [ -n "$status" ]; then
+            echo "ERROR: There are unexpected code changes" >&2
+            echo "$status" >&2
+            git diff >&2
+            exit 1
+          fi
+      - name: Run static checks
+        run: make lint
+      - name: Run tests
+        run: make test
+      - name: Test report
+        uses: dorny/test-reporter@v1
+        if: always()
+        with:
+          name: results-config-watcher-${{ matrix.python-version }}
+          path: test-results/reports/config_watcher.xml
+          reporter: java-junit
+          fail-on-error: true
+      - name: Upload test results
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: test-results-${{ matrix.python-version }}
+          path: |
+            test-results/config_watcher
+          retention-days: 7

.gitignore

@@ -168,4 +168,14 @@ cython_debug/
 #.idea/
 
 # PyPI configuration file
-.pypirc
+.pypirc
+
+# Temporary directories
+bin
+tmp
+
+# Test artifacts
+test-results
+
+# IDE specific files
+.vscode