fix(post-publish): handle Rush version bump in npm-post-publish pipeline

[iclanton]

Summary

• Fix issues with updates to rushstack-websites (prior commit): adds DisableInstallRunRushLockfile parameter to the install-run-rush.yaml template and uses it for the rushstack-websites stage, which doesn't have a lockfile checked in.

• Handle Rush version bump in post-publish pipeline (this commit): when bump-decoupled-local-dependencies updates the Rush version in rush.json, the subsequent rush update step would fail because install-run-rush.js tried to install the new Rush version while INSTALL_RUN_RUSH_LOCKFILE_PATH still pointed to the old version's lockfile.

  Fix:

  • BumpDecoupledLocalDependencies now emits RushWasUpdated (true/false) and NewRushVersion as Azure Pipelines variables, and only writes rush.json when the version actually changed.
  • If RushWasUpdated is true, a new conditional step bootstraps the new Rush version (skipping lockfile validation), then copies the new lockfile into common/config/validation/rush-package-lock.json before rush update runs — so rush update proceeds normally with a matching lockfile.

Test plan

• Verify the pipeline runs successfully when Rush is not updated (normal path unchanged)
• Verify the pipeline runs successfully when Rush is updated (new bootstrap steps trigger, rush update no longer fails)

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