Fix local docker image name for demos

[xfiderek]

Version or commit hash

23adec1

RMW Implementation

CycloneDDS

Steps to reproduce issue

1. Follow the tutorial for any of the demo dockers
2. Try building with space-ros:main
   

   docker/moveit2/README.md

   Lines 17 to 20 in 09ec444

   	```bash
   	# Use a locally built image as the base
   	SPACE_ROS_IMAGE="space-ros:main" ./build.sh
   	```

Expected behavior

The image name should be osrf/space-ros:main instead of space-ros:main

Actual behavior

The command fails because the image name is wrong.

Backtrace or Console output

No response