Show warnings when Azure AI Search is not configured

[MikeAlhayek]

@bleroy

This PR addressed the behavior you encountered in #14984. Basically, we register the services when the feature is enabled. But, if the configuration are missing from the file, then we show warning instead of showing action functions. Here is an example

[bleroy]

I'm sorry, I didn't have time to look at this before you merged it. The message doesn't give any clue about what needs to be configured. If you're going to the settings, chances are you're already trying to configure the search service, but don't necessarily know where to do it. The message should probably say that the Azure AI Search service needs to be specified in appsettings.json, and maybe even point to some documentation showing the exact format for that, or an example.
I'm also wondering how the feature could be used in hosted environments where you don't have access to the settings file. I'm not sure why all this can't be configured in the admin, including secrets. Then again I've been away from Orchard for a while now and I'm not sure how Core stores secrets in general.

[MikeAlhayek]

No worries. I'll update the message once we have clear path on #14989 . Once we support the described scenario the instruction will likely change so I'll make sure it is more descriptive.