Add GitHub Actions workflow for building Helm chart

This commit introduces a new GitHub Actions workflow defined in
`.gitea/workflows/build-chart-paperless-ngx.yml` to automate the
building and packaging of the Helm chart for the
Paperless-ng project. The workflow triggers on pushes to the
`main` branch when changes are made to the `charts/paperless-ngx/Chart.yaml`
file.

The key steps in this workflow include checking out the repository,
extracting the Helm chart's application name and version from the
`Chart.yaml`, setting up Helm, updating dependencies, linting the
chart, and finally packaging it.

The resulting Helm package is then uploaded to a specified Helm
registry using the credentials stored in the repository's secrets.
This automation is important for ensuring that the Helm chart
can be consistently and reliably built with each update, enhancing
the deployment process.

.gitea/workflows/build-chart-paperless-ngx.yml

@@ -0,0 +1,43 @@
+name: "Build Helm Chart"
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - "charts/paperless-ngx/Chart.yaml"
+
+jobs:
+  helm-package:
+    runs-on: ubuntu-latest
+    env:
+      APP: charts/pperless-ngx
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Set Helm Chart App Name and Version
+        id: get_version
+        run: |
+          APP_NAME=$(grep -oP '(?<=^name: ).*' ${{ env.APP }}/Chart.yaml)
+          echo "Helm Chart App Name: $APP_NAME"
+          echo "::set-output name=app::$APP_NAME"
+
+          CHART_VERSION=$(grep -oP '(?<=^version: ).*' ${{ env.APP }}/Chart.yaml)
+          echo "Helm Chart version: $CHART_VERSION"
+          echo "::set-output name=tag::$CHART_VERSION"
+
+      - name: Setup Helm
+        run: |
+          #curl https://raw.githubusercontent.com/helm/helm/main/scripts/get-helm-3 | bash
+          curl -kSso /usr/local/bin/helm https://debmirror.cooltux.net/helm-v3.18.4 && chmod +x /usr/local/bin/helm
+          helm version
+
+      - name: Package Helm Chart
+        run: |
+          helm dependency update ${{ env.APP }}
+          helm lint ${{ env.APP }}
+          helm package ${{ env.APP }}
+
+      - name: Upload Helm Package to repo
+        run: |
+          curl --user ${{ secrets.USER }}:${{ secrets.TOKEN }} -X POST --upload-file ./${{ steps.get_version.outputs.app }}-${{ steps.get_version.outputs.tag }}.tgz ${{ vars.HELMREGISTRY }}/api/packages/${{ vars.OWNER }}/helm/api/charts