Add migration script for Ghost CLI -> Docker installs

- This script handles the copy of both assets and the MySQL database
  from an existing install to a new Docker based install
- Its currently been tested on the "happy path" of a Ghost CLI install
  and works

.github/workflows/shellcheck.yml

@@ -0,0 +1,16 @@
+---
+name: "ShellCheck"
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+jobs:
+  shellcheck:
+    name: ShellCheck
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Run ShellCheck
+      run: find . -type f -name "*.sh" -exec shellcheck {} +