Consider adding workspace members as sources in `uv init`

Initializing as workspace member adds it to the root package workspace members but does not add it as a dependency, e.g.:

❯ uv init
❯ uv init foo
Adding `foo` as member of workspace `/Users/zb/workspace/example`
Initialized project `foo` at `/Users/zb/workspace/example/foo`
❯ cat pyproject.toml
[project]
name = "example"
version = "0.1.0"
description = "Add your description here"
readme = "README.md"
requires-python = ">=3.12"
dependencies = []

[tool.uv]
dev-dependencies = []

[tool.uv.workspace]
members = ["foo"]

uv add will do so:

❯ uv add foo
❯ cat pyproject.toml
[project]
name = "example"
version = "0.1.0"
description = "Add your description here"
readme = "README.md"
requires-python = ">=3.12"
dependencies = [
    "foo",
]

[tool.uv]
dev-dependencies = []

[tool.uv.workspace]
members = ["foo"]

[tool.uv.sources]
foo = { workspace = true }

We should something like:

• Add a toggle to control adding to the current workspace in a single invocation
• Determine the default behavior
• If not added by default, show a hint suggesting how to add it