Be able use pnpm with static Web Apps CI/CD Actions - https://github.com/Azure/static-web-apps-deploy

**Is your feature request related to a problem? Please describe.**
I have an existing build of pnpm based build Next.js 15 and I wanted to reuse it when deploying Azure Static Web Apps. I used the `skip_app_build` option with https://github.com/Azure/static-web-apps-deploy, but this wasn't enough and it failed with timeout during the warmup phase.

**Describe the solution you'd like**
It would be great if there's a clean & officially supported way to reuse our existing CI/CD pnpm based build as part of our CI/CD to Azure Static Web Apps GitHub action

**Describe alternatives you've considered**
- The workaround here really helped (https://github.com/azure/static-web-apps/issues/1457). We have added `.npmrc` file to the project with the following content. However this is known to be a workaround and has potential issues.
```
shared-workspace-lockfile=false
node-linker=hoisted
```

This was used with the `skip_app_build` option to skip the build.

**Additional context**
- If the workaround from the https://github.com/azure/static-web-apps/issues/1457 is the recommended solution, please update documentation, so it's clear for developers