This change migrates plugin config format away from using JSON to use
TOML.
- Addresses the plugin portion of discussion #1336
## Type of Change
- [ ] Bug fix
- [X] New feature
- [ ] Breaking change
- [ ] Documentation update
## Motivation and Context
Context within https://github.com/apple/container/discussions/1336
> We're looking to improve the user experience and overall functionality
of setting defaults for container to better enable future use cases.
>
> Today container uses macOS's
[UserDefaults](https://developer.apple.com/documentation/foundation/userdefaults)
to configure settings needed at runtime. As mentioned in
https://github.com/apple/container/issues/608, UserDefaults may be
idiomatic for macOS, but they apply globally to all sessions and do not
handle representing complex, hierarchical data well. Additionally, we
currently have two ways of setting these defaults, either directly with
macOS's defaults command or through container system property.
>
> https://github.com/apple/container/issues/608 proposes moving to use
environment variables in place of UserDefaults. However, we do not
believe this is sufficient. Environment variables are not in a
consistent location, are not sourced from data, and also do not handle
representing complex, hierarchical data well.
As part of this migration to TOML for user settings we want to also move
plugin settings to use TOML so that we can have a singular file format
for `container` configurations.
## Testing
- [X] Tested locally
- [X] Added/updated tests
- [ ] Added/updated docs
## Type of Change
- [x] New feature
- [x] Breaking change
## Motivation and Context
This PR changes the behavior of the `defaultArguments` field in the
service plugin config. Previously, `defaultArguments` was functioning as
a way to indicate how to start a plugin in the event that the plugin is
loaded at boot (such as for the `container-core-images plugin`).
However, we now follow a convention where all plugins have a "start"
command that is used when launching the plugin, so this
`defaultArguments` field wasn't really providing much. Instead, there
are use cases where we may want to set default values to pass to a
plugin. This PR repurposes the `defaultArguments` field for those use
cases.
As an example use case, there are scenarios where someone may want to
use the AllocationOnlyVmnetNetwork even when running on macOS 26+. This
PR adds the ability to pass in a command line option to the vmnet
network plugin to specify that request. Combined with the
`defaultArguments` plugin config change, a user may choose to set that
field to ["--variant", "allocationOnly"] in the
`container-network-vmnet-config.json` to use AllocationOnlyVmnetNetwork
by default for all networks.
## Testing
- [x] Tested locally
Noah Thornton