Implement Powershell templates workload

Original issue tracked at https://github.com/Azure/azure-functions-core-tools/issues/5323. Content copied over:

Add the PowerShell templates workload covering the basic triggers (HTTP,
timer, queue, blob) so `func new` produces working PowerShell functions
under the v5 workload model.

## Definition of Done

- [ ] Templates workload nupkg builds and publishes via the workloads
pipeline.
- [ ] CI pipeline (public + official/signed) wired up for the workload.
- [ ] `func new` surfaces HTTP, timer, queue, and blob templates for
PowerShell.
- [ ] Each generated template builds and runs locally via `func start`.
- [ ] Templates manifest validated by the schema in CI.

Read the existing workloads pipeline and templates manifest first, then exercise `func new` for the HTTP, timer, queue, and blob PowerShell triggers. Done means the workload nupkg publishes, public and official/signed CI runs, the manifest passes schema validation, and each generated template builds and runs with `func start`.

Written by the indexing model from the issue text.