fixup the demo documentation for the image_pipeline_demo (backport #6041)

[mergify]

Description

The code for the image_pipeline_demo (part of the intra_process_demo package) has been wrong for a long time and the documentation was self-contradicting for some time as well. This pull request, in addition to ros2/demos#755, restores the demo to its intended behavior and cleans up the documentation here about it.

I also changed our use of intra process/interprocess to be intra-process/inter-process everywhere, as that is more consistent and it is consistent with other sources on this topics, e.g. https://en.wikipedia.org/wiki/Inter-process_communication which uses inter-process, and our own documentation where we use intra-process commonly.

Requires ros2/demos#755

Fixes #2333

Did you use Generative AI?

No.

Additional Information

This replaces another pull request #5988, which was trying to fix this, but didn't realize the demo was actually subtly broken, not the docs.

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This is an automatic backport of pull request #6041 done by Mergify.

[github-actions]

HTML artifacts: https://github.com/ros2/ros2_documentation/actions/runs/19645024354/artifacts/4664310981.

To view the resulting site:

1. Click on the above link to download the artifacts archive
2. Extract it
3. Open html-artifacts-6048/index.html in your favorite browser

[wjwwood]

Waiting for ros2/demos#758 to be merged.