upgrade - add a way to downgrade from prerelease to the latest official version

I sometimes upgrade my company's package on my PC to prerelease version (for a review etc.) and then I want to bring official version back. I have two options:
- Uninstalling and installing the package again without `--pre` flag (performs scripts even if I already am on official version),
- Upgrading to specific official version (requires checking version's number).

I would like to have the third option without drawbacks of the two above, going something like:
`choco upgrade package-name --allow-downgrade --exclude-prerelease`
**Current:**
> package-name v1.0.1-pre is newer than the most recent.
You must be smarter than the average bear...

**Expected:**
> You have package-name v1.0.1-pre installed. Version 1.0.0 is available based on your source(s).

Another flag like "official-only" would also work for me.
Discussion in #686 makes sense to me, but refers to situation when before upgrade there is a package installed that is older than the latest official. In my case, installed package is newer than the latest official.

Start with the upgrade command and its handling of --allow-downgrade and prerelease versions, then read the referenced discussion in #686 for related behavior. Define the version-selection and script-execution cases around an installed prerelease; done means the command selects the latest official version and reports it as expected without the stated drawbacks.

Written by the indexing model from the issue text.