Issue an actionable warning on CommandNotFoundException

[AnatoliB]

Problem
When users try to invoke a command that cannot be found in any modules, they get just the standard PowerShell error: The term 'xxx' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again. Sometimes they do get into this situation because of a typo, but very often this happens because they are missing modules, or because these modules don't work in PowerShell Core. It takes time and effort to realize that, and then it takes time and effort to figure out how to make the required modules available. Even though we have this documented, the documentation is not immediately discoverable, so new Function users spend more time and effort to invent their own ways, and sometimes come up with inefficient and difficult to support solutions.

Proposal

• Detect this error during function execution and log a warning with suggestions and documentation links, something like: The app may be missing a module containing the 'xxx' command definition. If this command belongs to a module available on the PowerShell gallery, add a reference to this module to requirements.psd1. Make sure this module is compatible with PowerShell Core 6 or PowerShell 7. For more details, see <doc link>. /cc @eamonoreilly for the message wording.
• Consider going further: query the PS Gallery automatically and come up with a line of code to be inserted into requirements.psd1, include this line into the warning text.

[AnatoliB]

A similar issue: When the function invokes Import-Module for a module that has not been installed into the app, the error message from PowerShell is: Import-Module : The specified module 'xxx' was not loaded because no valid module file was found in any module directory.

This message is also not clear and actionble for new Function users. We could detect this error and issue an additional warning: The app may is missing the 'xxx' module. If module 'xxx' is available on the PowerShell gallery, add a reference to this module to requirements.psd1. Make sure this module is compatible with PowerShell Core 6 or PowerShell 7. For more details, see <doc link>.