[IMP] add external command verification at startup

Add check_required_commands() function to verify that all required
external tools are available before the script begins execution:
- docker: Container runtime
- compose: Docker compose wrapper (0k-scripts)
- sudo: Required for filestore operations

Benefits:
- Fails fast with a clear error message listing missing commands
- Prevents cryptic 'command not found' errors mid-execution
- Documents script dependencies explicitly
- Called immediately after argument validation in upgrade.sh

upgrade.sh

@@ -29,6 +29,8 @@ if [[ $# -lt 4 ]]; then
     usage
 fi
 
+check_required_commands
+
 readonly ORIGIN_VERSION="$1"
 readonly FINAL_VERSION="$2"
 readonly ORIGIN_DB_NAME="$3"