Expose different uv index resolution strategies

[tdejager]

Problem description

UV currently support different index resolution strategies, see this: astral-sh/uv@main/PIP_COMPATIBILITY.md#packages-that-exist-on-multiple-indexes

Pixi currently supports the default option, which is similar to strict index priority in conda. For some users, this has proved too limiting: https://github.com/prefix-dev/pixi/issues/1373

I propose having this option exposed through the [pypi-options] table, this would be an exclusive option per solve-group/environment.