[Extensions] "Blessed" Extensions should not trigger warnings when overriding existing commands

[tjprescott]

As discussed via email, official or "blessed" extensions should suppress the warning about overriding the default implementation.

[digimaun]

Thanks for creating the issue we discussed @tjprescott. The IoT extension can be a guinea pig for blessing criteria.

[troydai]

The difficulty of assigning an extension the 'blessed' status is that there is no way to verify the identity of an extension. We don't sign the extension.

[derekbekoe]

With an extension index, we could have control over such blessed extensions.

[JasonRShaver]

Currently this is by design, especially given the relative scope of extensions. As the CLI grows, we'll revisit this to setup some healthy and secure patterns here. If you have any user data or complains, please share with us to help us prioritize.

[jongio]

@johanste - The message is pretty intimidating and for the IoT extension, we'd like to have something more friendly or nothing at all. Can we revisit this?

[yonzhan]

add to S165.

[jiasli]

We have added option --only-show-errors in #12604 to disable warnings that are written to stderr. It will be included in S167 release.