Enable first-class non-interactive mode for the CLI

I'm a fan of `dnx` but have found that there are some usability issues with LLMs. The basic problem is that it requires an interative response, which causes a non-interactive user to just hang. I have noticed this a couple times recently. However, I was writing a skill that uses a tool and wanted to use `dnx`. However, using `dnx` is challenging. We need good guidance for this and to consider product changes. For now I'm saying, always use `dnx -y dotnet-inspect -- [args]`.

There are two cases where an LLM might hit an interactive prompt:

- First install
- New version available

The second point is the most challenging. A session could be moving forward using a tool and then a new version is published to nuget.org, `dnx` notices this, and then blocks the LLM (or other tool) with an interactive prompt. This also means that `dnx` isn't a great choice for scripts, as-is.

Here's what I see.

DNX:

NPM:

This is from `npm exec help`:

> If any requested packages are not present in the local project
> dependencies, then a prompt is printed, which can be suppressed by
> providing either --yes or --no. When standard input is not a TTY or a CI
> environment is detected, --yes is assumed. The requested packages are
> installed to a folder in the npm cache, which is added to the PATH
> environment variable in the executed process.

I asked Copilot to thoroughly test this:

I don't think that stdin is excellent solution. It's a pattern to enable. I'd like to see the dnx offer the same model as npx and also offer an ENV variable to make a whole session safe. That would mean install the package if not available and DON'T install a new package if one is available unless asked to.

Side note: We should make it easy to clear the dnx cache. This made testing a bit awkward.

I sometimes see the first-run experience in CP-CLI/CC. This is harmful, in the sense that it is wasted tokens and the person we wanted to see the first-run experience doesn't. Assuming we a `DOTNET_INTERACTIVE=false`, then I'd skip the first-run message as well. There may be other experiences we need to consider. That's why the title is about the scenario not dnx in particular.