Add gestures to manage extension bundles

Allow setting the extension bundle version. Something like:
```bash
func extensions use-bundles --version 2
```

If extensions.csproj is currently used, warn and ask to confirm, then remove `bin/`, `obj/`, `extensions.csproj` and configure host.json with bundles.

When `func extensions install` is run with bundles configured, warn and ask to confirm. If accepted, remove bundles and continue with extensions install.

Start by locating the command handlers for `func extensions use-bundles` and `func extensions install`, then inspect how `extensions.csproj`, `bin/`, `obj/`, and `host.json` are currently handled. Done means version selection, confirmation prompts, removal of the conflicting configuration when accepted, and continued installation behavior match the issue description.

Written by the indexing model from the issue text.