[Doc] Clarify the relation between 'uv run' and 'uv pip' support

[pcmoritz]

Why are these changes needed?

Fixes #51195

Related issue number

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[crypdick]

lgtm

[edoakes]

@pcmoritz should we continue to support both?

[pcmoritz]

Given that uv supports both it seems natural that we do so too -- if uv run turns out to be much more popular I'd be open to remove uv pip.

Do we currently have telemetry on which runtime environment plugins are used? We can distinguish them via uv vs. py_executable :)

[edoakes]

Do we currently have telemetry on which runtime environment plugins are used? We can distinguish them via uv vs. py_executable :)

Not atm but it can be added