simpler instructions for migrations

Sometimes my organisation does PR campaigns to migrate things, like from one registry to another. It helps to package migration guide into an gh extension, so those extensions can be run in the migration pr campaign and by developers. If you need a second run, extension can be outdated, so you have to ask people to upgrade the extensions. All of it complicates instructions, where single one liner can do its job

Proposed solution

First of all we need to combine install and exec into one command and then we need to prevent execution of outdated extensions. install and exec combination can be in a form of ghx or gh extension ix. Prevention of outdated extension execution can be done in a form of --no-cache or --latest flags

ghx owner/gh-ext --latest
# or
gh extension ix owner/gh-ext --latest
# or
gh extension install-exec owner/gh-ext --latest

Additional context

npx is widely popular in node community and this change bring the same spirit to a wider community of more languages and ecosystems.