Our previous workflow for running a specific set of prepare-dev.py was

to to pass an argument for each section we did not want to run. e.g., to

run only the dependency installation, you would run:

./contrib/internal/prepare-dev.py --no-db --no-media.


That is, each action was enabled by default and you had to disable

everything you didn't want to run. As more features get added to

prepare-dev.py, it becomes less user friendly to force the user to

specify the complement of the features that they don't want to run.
Now we have an --only option which inverts our usual behaviour. In

other words, to run only the dependency installation as above, you

would run

./contrib/internal/prepare-dev.py --only --deps


This allows the user to more easily specify and run a minimal part of

prepare-dev.py's actions, as opposed to the old behaviour which

assumed you wanted to run a maximal part of its actions.

Ran ./contrib/internal/prepare-dev.py --only --deps and only deps

were installed.