[rush] Expected that the rush update-autoinstaller command can sync the rush-plugins manifest.json files to the rush-plugins directory

[LPegasus]

Summary

Currently, after running rush update-autoinstallers, the rush-plugin-manifest.json file is not copied to rush-plugins directory. Instead, it requires running rush update to trigger the sync of this file. This is somewhat counterintuitive in terms of usage.

Meanwhile, during development, it can also easily lead to the omission of the rush-plugin-manifest.json file. The development process is as follows:

1. Develop the plugin locally and declare it in autoinstallers/rush-plugins/package.json using link:./<path_to>/my-rush-plugin.
2. After testing is completed, the my-rush-plugin/rush-plugin-manifest.json file has already been saved in the git repository.
3. Assuming that the rush-plugin-manifest.json file is not declared in the files field of my-rush-plugin's package.json, it is difficult for CI to detect this issue at this point. This is because CI usually runs the install command, and only rush update can identify this problem.

If rush update-autoinstaller tried to copy the manifest files, than in the update pnpm-lock.yaml step, the problem will be detected.

Repro steps

Run rush update-autoinstaller --name rush-plugins

Expected result: The rush-plugin-manifest.json files will be copied to the rush-plugins directory.

Standard questions

Please answer these questions to help us investigate your issue more quickly:

Question	Answer
@microsoft/rush globally installed version?	5.155.1
rushVersion from rush.json?	5.155.1
useWorkspaces from rush.json?	Yes
Operating system?	Mac
Would you consider contributing a PR?	Yes
Node.js version (node -v)?	22.20.0