pkg_rpm documentation inconsistent with test example

The `pkg_rpm` invocation in https://github.com/bazelbuild/rules_pkg/blob/main/pkg/tests/rpm/BUILD shows a lot more options than the doc at https://github.com/bazelbuild/rules_pkg/blob/main/pkg/docs/reference.md#pkg_rpm. Which one is correct (probably neither :) )

Compare the `pkg_rpm` invocation in `pkg/tests/rpm/BUILD` with the `pkg_rpm` reference in `pkg/docs/reference.md`. Determine which options and example are current, then make the documentation and test example consistent and verify the resulting example still matches the documented interface.

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