[rush-lib] Prioritise new subspace config via a new .npmrc template file

[pedro-gomes-92]

Summary

Applies more accurate subspace configurations via rush init-subspace

Details

When creating a new subspace via rush init-subspace, the rush .npmrc template might not be proper for the specific subspace. Instead it should rely on a empty .npmrc, so that the subspace can initially use the same configuration as the monorepository, i.e. common/config/rush/.npmrc.

How it was tested

• Create a repository with subspaces enabled: https://rushjs.io/pages/advanced/subspaces/
• Run rush init-subspace --name test

Check the common/config/subspaces/test/.npmrc contains an empty configuration.