Stop using npmrc to consume internal packages

[hallipr]

To prepare for eng/common changes that will no longer create ephemeral .npmrc files when emitter-package.json contains "-alpha", we need to remove our dependency on the npmrc files in favor of url based alpha package versions.

• Use new emitter-package-json creation scripts to avoid npmrc usage in azure-sdk-for-net while still directing alpha packages to the internal feed
• Use proper leg naming in the matrix. The existing names contained invalid characters
• Include the leg key as a leg variable so we can use it in the resulting commit message
• Update emitter-package-json files and Package.Data.props in an initial commit to the PR branch, then reuse that branch as the source for the generation legs instead of sourcing from 'main'
• Make the variable names used for package versions in build.yml and sdk-update.yml more consistent