Currently, the only way to pass information to cargo-subspace is via CLI flags. This is fine and dandy in many cases, but there will be situations where it's useful to tailor the arguments to the workspace you're currently working in. Some of these situations could include:

• Passing different feature flags based on the current workspace
• Choosing to use check or clippy on a per-workspace basis
• Passing different arguments to check or clippy based on the current workspace
• If we eventually support "manual mode" (see Support "manual mode" #18), this would need to be set on a per-workspace basis

I think it would be useful to introduce an optional per-workspace configuration file (maybe something like cargo-subspace.toml?) to store such options. Maintainers or project owners could choose to check in this file to version control if they wanted to standardize certain behavior (e.g. feature flags or check/clippy). Alternatively, people could choose to add the file to .gitignore to use their own configuration.