WebGPU plugin EP pipeline updates (#28121)
### Description
<!-- Describe your changes. -->
- Fix issue with custom .npmrc file not being found by
tools/ci_build/github/linux/build_webgpu_plugin_package.sh (follow up to
#28079)
- Set build-enabled parameters to true by default
- Configure nightly build in yaml
- Remove unnecessary NPM configuration in Windows build - now, it is
handled by templates/setup-build-tools.yml
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
Fix pipeline issue. Build all supported platforms nightly.
