Move images to solutions folder

[lcawl]

Relates to #1079

This PR moves the files from the top-level images folder to the appropriate solutions/images folder, since they were broken in the former location.

I've also moved observability-apm-app-landing.png to address the following warning:

Warning: Image '/reference/images/observability-apm-app-landing.png' is referenced out of table of contents scope '/home/runner/work/docs-builder/docs-builder/test-repo/reference/apm'.
    ┌─[/home/runner/work/docs-builder/docs-builder/test-repo/reference/apm/observability/apm.md]