Rename `PythonRequest::Any` -> `PythonRequest::Default` (#7514)
As we support more complex Python discovery behaviors such as:
- #7431
- #7335
- #7300
`Any` is no longer accurate, we actually are looking for a reasonable
default Python version to use which may exclude the first one we find.
Separately, we need the idea of `Any` to improve behavior when listing
versions (e.g., #7286) where we do actually want to match _any_ Python
version. As a first step, we'll rename `Any` to `Default`. Then, we'll
introduce a new `Any` that actually behaves as we'd expect.
