Add default-packages = [...] and default-packages = "all" for workspaces

[zanieb]

We should consider allowing setting the default sync packages as we do for dependency groups.

People should be able to set the default sync packages without adding them as explicit project dependencies. I guess they could add them to a dependency group, but that doesn't address the all case. default-packages = "all" would be equivalent to --all-packages.

Related

• Better default for uv sync #10934
• Decide on semantics for workspace environment syncing (with --package, --extra, and --dev) #4730
• Sync a subset of packages, but not all #12130

[zanieb]

cc @@Tremeschin