[rush-lib] Prioritise new subspace config via rush repository config

[pedro-gomes-92]

Summary

Applies more accurate subspace configurations via rush init-subspace

Details

When creating a new subspace via rush init-subspace, the subspace configuration templates might not be proper for the specific working repository. Instead we should prioritise the rush repository configurations from common/config/rush (if exists), which are more accurate for the repository.

How it was tested

• Create a repository with subspaces enabled: https://rushjs.io/pages/advanced/subspaces/
• Update the configuration common/config/rush/.npmrc
• Run rush init-subspace --name test

Check the common/config/subspaces/test/.npmrc contains your new changes.