Include default command settings in stack config file

[ncoghlan]

There are several locking, build, and publishing settings which could reasonably be considered part of the stack specification:

• package index access settings (especially once Allow specification of package index URLs #144 has been implemented)
• whether to produce tagged or untagged outputs
• where to find additional local wheel archives
• locking mode to use (once Add a "comprehensive" locking mode #2 has been implemented)
• default locations for working and output artifact directories

While settings these globally or per-user doesn't necessarily make sense (although #20 would allow that to some degree), it does make sense to allow the stack specification file to include a [config] section which changes the default values used for various settings.

https://maxb2.github.io/typer-config/latest/ may be a useful dependency to consider for this purpose (as this idea would be similar to the "pyproject.toml section" approach described in https://maxb2.github.io/typer-config/latest/examples/pyproject/ )

[ncoghlan]

Another good candidate for inclusion as a stack config setting:

• Support publication of gzip tar archives #90

[ncoghlan]

I'm currently leaning against tightly coupling the config file processing with the CLI option processing, since some of the settings I'd like to be configurable at the project level don't really make sense as CLI options:

• marking an entire stack definition file as platform specific
• choosing a locking mode (if that ends up being configurable instead of simply changing the locking algorithm)
• choosing a layer archiving mode (as per Add a "conceptual" layer archiving mode #146)