develop -> command is inconsistent with rest of BUILD.yaml config

[fbarl]

Looking through different brick BUILD.yaml files, I noticed that in some steps command is used while in some others there is a list of commands. I assumed the two are actually interchangeable and that both can be used across build, test, develop etc, only to end up trying to figure why test -> command config is always passing the tests - turns out the commands list being empty means no command have been run so it always passes.

Looking at the code, it seems that only develop uses a singular command while all the other steps require commands. I have a few suggestions how we could improve the behaviour:

1. Switch to commands syntax in develop and completely drop the command option
2. Support both command and commands options across all steps
3. Keep things as they are but document the examples better to make it clear develop steps are an exception in the sense that only there exactly one command is expected

See https://github.com/tmrowco/tmrow/issues/3236 for more context.

[corradio]

Good catch! I think the best solution is to support both. That would make sure the tool stays intuitive!