Update ADO task and GitHub Actions workflow to support v5 CLI

Update the ADO pipeline task and GitHub Actions workflow to support installing and using the v5 CLI.

This includes:
- **ADO pipeline task:** [`AzureFunctionApp@v1/v2`](https://github.com/microsoft/azure-pipelines-tasks/tree/master/Tasks/AzureFunctionAppV2) in `microsoft/azure-pipelines-tasks` — ensure it can install v5 from CDN
- **GitHub Actions:** [`Azure/functions-action`](https://github.com/Azure/functions-action) — support v5 CLI installation
- Both should respect the single-install-location guidance (don't conflict with other install methods)

GA-blocking — CI/CD pipelines are a primary consumption path for the CLI.

From the [CLI release design](https://github.com/Azure/azure-functions-core-tools/pull/5391).

Start with the CLI release design in PR 5391, then inspect the AzureFunctionApp@v1/v2 task in microsoft/azure-pipelines-tasks and the Azure/functions-action repository. Trace their CLI installation paths and CDN usage; done means both integrations can install and use v5 while respecting the single-install-location guidance without conflicts.

Written by the indexing model from the issue text.