Initial cruft update workflow

.cruft.json

@@ -0,0 +1,28 @@
+{
+  "template": "https://github.com/CyclingNinja/packaging-guide",
+  "commit": "8fbd8e7825ca747dece08c592965570403e25fec",
+  "checkout": null,
+  "context": {
+    "cookiecutter": {
+      "package_name": "test_sub_package",
+      "module_name": "sub_package",
+      "short_description": "a package",
+      "author_name": "sam bennett",
+      "author_email": "[email protected]",
+      "license": "BSD 3-Clause",
+      "project_url": "a_project.com",
+      "minimum_python_version": "3.8",
+      "use_compiled_extensions": "n",
+      "include_example_code": "y",
+      "_sphinx_theme": "alabaster",
+      "_parent_project": "",
+      "_install_requires": "",
+      "_copy_without_render": [
+        "docs/_templates",
+        "docs/_static"
+      ],
+      "_template": "https://github.com/CyclingNinja/packaging-guide"
+    }
+  },
+  "directory": null
+}

.github/workflows/sub_package_update.yml

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+name: Update SunPy Sub Packages
+permissions:
+    contents: write
+    pull-requests: write
+
+on:
+  pull_request:
+    branches:
+      main
+jobs:
+  update:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: true
+      matrix:
+        include:
+          - add-paths: .
+            body: Use this to merge the changes to the repo
+            branch: cruft/update
+            commit-message: "SunPy package template update"
+            title: New Updates to SunPy Template
+          - add-paths: .cruft.json
+            body: Use this to reject changes in the repo
+            branch: cruft/reject
+            commit-message: "Chore: reject this cruft update"
+            title: Reject new SunPy template updates
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - uses: actions/setup-python@v4
+        with:
+          python-version: "3.10"
+
+      - name: Install Cruft
+        run: pip3 install cruft
+
+      - name: Check if update is available
+        continue-on-error: false
+        id: check
+        run: |
+          CHANGES=0
+          if [ -f .cruft.json ]; then
+            if ! cruft check; then 
+              CHANGES=1
+            fi
+          else
+            echo "No .cruft.json file"
+          fi
+          
+          echo "has_changes=$CHANGES" >> "$GITHUB_OUTPUT"
+
+      - name: Run update if available
+        if: steps.check.outputs.has_changes == '1'
+        # this needs to be sunpy details I think?
+        run: |
+          git config --global user.email ""
+          git config --global user.name "SunPy Org"
+          
+          cruft update --skip-apply-ask --refresh-private-variables
+          git restore --staged
+
+      - name: Create pull request
+        if: steps.check.output.has_changes == '1'
+        uses: peter-evans/create-pull-request@v4
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          add-paths: ${{ matrix.add-paths }}
+          commit-message: ${{ matrix.commit-message }}
+          branch: ${{ matrix.branch }}
+          delete-branch: true
+          branch-suffix: timestamp
+          title: ${{ matrix.title }}
+          body: |
+            This is an autogenerated PR. ${{ matrix.body }}
+              [Cruft](https://cruft.github.io/cruft/) has detected updates from the SunPy Package Template 
+