Add npmFeed parameter and shared variables template to pipeline templates

[Copilot]

Threads npmFeed through both ADO pipeline templates so they can resolve packages from internal NPM feeds via the shared vscode-azuretools template parameter.

Changes

• .config/build.yml — add shared AZCode variables template reference (azdo-pipelines/azcode.variables.yml@azExtTemplates) and npmFeed: ${{ variables.npmFeed }} to extends.parameters
• .config/release.yml — add npmFeed: ${{ variables.npmFeed }} to extends.parameters

The npmFeed variable is sourced from azdo-pipelines/azcode.variables.yml@azExtTemplates, which is now included in both pipeline configs.

Original prompt

In this repository, add the npmFeed parameter to the Azure DevOps pipeline templates in .config/build.yml and .config/release.yml. Specifically: In .config/build.yml, add 'npmFeed: ${{ variables.npmFeed }}' as a new line under the 'extends.parameters' section (at the end of the parameters list). In .config/release.yml, add 'npmFeed: ${{ variables.npmFeed }}' as a new line under the 'extends.parameters' section (at the end of the parameters list). This enables the pipelines to use internal NPM feeds. See microsoft/vscode-containers#471 for reference.