Detect ondemand dir instead of hardcoding

[Bubballoo3]

Fixes #5463. Searches for a directory named 'ondemand' in the ancestry of the working directory. Defaults to pwd if no directory named 'ondemand' is found

[Bubballoo3]

Moving this to a draft as I believe it is disrupting to installed gems if the path changes for the mounted directory. I think this will still be useful though eventually, as the path resolution will have to be fixed to support macOS, where the home directory is /Users/username instead of /home/username. So we will have to find some symlinking approach where you can have a copy of the code in /home/username/ondemand inside the container, but also maintain a copy at the original path (`/Users/username/code/ondemand, eg) and build paths still resolve.

[Bubballoo3]

This ended up working out how I expected, where we mount the detected ondemand dir at the same path as the original, but then create a symlink to the location ondemand expects it to be. This way the gems and files of the built development dashboard carry over to the container, allowing you to enter and boot up the dev container without modification.