fix: Fix provisioned-instance Dockerfile COPY paths for build context

The docker-security-scan.yml workflow uses context: docker/provisioned-instance
for the provisioned-instance image, which means COPY paths should be relative
to that directory, not include the full path from root.

Changed:
- COPY docker/provisioned-instance/supervisord.conf → COPY supervisord.conf
- COPY docker/provisioned-instance/entrypoint.sh → COPY entrypoint.sh

This matches the build context pattern used for backup and other images.

Author: josecelano

docker/provisioned-instance/Dockerfile

@@ -80,10 +80,10 @@ EXPOSE 22
 WORKDIR /home/torrust
 
 # Create supervisor configuration
-COPY docker/provisioned-instance/supervisord.conf /etc/supervisor/conf.d/supervisord.conf
+COPY supervisord.conf /etc/supervisor/conf.d/supervisord.conf
 
 # Create entrypoint script for initialization
-COPY docker/provisioned-instance/entrypoint.sh /usr/local/bin/entrypoint.sh
+COPY entrypoint.sh /usr/local/bin/entrypoint.sh
 RUN chmod +x /usr/local/bin/entrypoint.sh
 
 # Set entrypoint