Add inbound agent pictures

[MarkEWaite]

Add pictures for inbound agent documentation

Fix #767

From https://github.com/jenkinsci/docker-inbound-agent.git

Testing done

Confirmed that the images render as expected in the pull request.

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[lemeurherve]

Good catch thanks!

Missed this folder while merging both repos in #570

[MarkEWaite]

@lemeurherve thanks! I skipped one image (0.jpg) that was in the root directory and seemed to be unused. If we discover a location where it is used, we can add it to the repository as well.