Improve install_cert.sh: validation, backup, and UX enhancements

[DerekRoberts]

Suggestions for install_cert.sh improvements

1. File existence and format validation

   • Check that ${DOMAIN}.pem, ${DOMAIN}.key, and ${DOMAIN}.ca-cert exist and are non-empty before proceeding.
   • Optionally, use openssl to verify that the certificate and key match (modulus check).

2. Automatic route backup

   • Before making any changes, export the current route YAML to a timestamped backup file (e.g., using: oc get route -o yaml > backup).
   • This allows quick rollback if something goes wrong.

3. Safer route replacement

   • If the route already exists, handle it gracefully (e.g., use oc replace, oc apply, or delete the old route first).
   • Echo a clear error message if route creation fails.

4. CA chain handling

   • If the CA chain is split across multiple files, concatenate them into ${DOMAIN}.ca-cert before running the script.

5. User experience improvements

   • Echo the full oc command before running it so the user can see exactly what will be executed.
   • Add clear error messages and confirmations at each step.

These changes will make the script safer, more robust, and easier to use and recover from errors.