Moved defaults away from argparser to `defaults.py`. This unlocks the ability to
pass values that can be defined as command line arguments via a config file.
With this change logic looks like this (in order of overrides).
Pre-build config:
`data/defaults.toml` -> `build-flavors/<flavor>.toml` ->
`--<command line argument>`
Build config:
`defaults.py` -> `data/defaults.toml` -> `build-types/<type>.toml` ->
`architectures/<architecture>.toml` -> `build-flavors/<flavor>.toml` ->
`--<command line argument>`
