Add feedBaseUrl parameter to 1ES build pipeline (Phase A)

[bwateratmsft]

Summary

Add the feedBaseUrl parameter to this repo's 1ES build pipeline so it is passed into the shared Azure DevOps build template. This is Phase A of the npm private-feed migration tracked in microsoft/vscode-azuretools#2320.

Exact change

Edit .config/build.yml only. In the extends: → parameters: block, add this line directly alongside the existing npmFeed line:

    feedBaseUrl: ${{ variables.feedBaseUrl }}

So a block that currently looks like:

extends:
  template: azdo-pipelines/1es-mb-main.yml@azExtTemplates
  parameters:
    npmFeed: ${{ variables.npmFeed }}

becomes:

extends:
  template: azdo-pipelines/1es-mb-main.yml@azExtTemplates
  parameters:
    npmFeed: ${{ variables.npmFeed }}
    feedBaseUrl: ${{ variables.feedBaseUrl }}

Important constraints

• Do NOT remove npmFeed. This change is purely additive — both parameters must be present after this change.
• The feedBaseUrl variable is already available: the file imports it via the shared azdo-pipelines/azcode.variables.yml@azExtTemplates template (the same source as npmFeed). No other file needs to change.
• Change only .config/build.yml. Do not modify any other files, and keep the edit minimal (a single added line).
• If the extends block is split across ${{ if ... }} conditions, add feedBaseUrl at the same top level as npmFeed (an unconditional parameter), not inside a conditional.

Why

The shared template is migrating private-feed routing from the legacy npmFeed (feed name) to feedBaseUrl (feed base URL). Adding feedBaseUrl now is safe under the current template (it is only used for test env vars today) and is a prerequisite before the template flips to feed routing via feedBaseUrl. See microsoft/vscode-azuretools#2320 for the full plan.