Move cibw config to pyproject.toml

[emlowe]

Puts most cibuildwheel configuration into pyproject.toml instead of using envvars in the github actions.

The rationale is that this makes it a little bit easier to build the wheel locally for debugging and testing as there is less configuration specific to GH actions

Note some of the envvars refer to GH action matrix items, so those remain in the GH workflow.