Investigate if we could de-hardcode /usr/src/app

_Originally posted by @jvanulde in https://github.com/OpenDRR/model-factory/pull/96#discussion_r787968634_

> @jvanulde: We should avoid system paths.
> @drotheram: Pass the path as an argument?
> @jvanulde: Probably best.

See also OpenDRR/opendrr-api#114