Notify user if physical table is missing

[khtruong]

Describe the solution you'd like
When a user goes to edit the datasource in a chart, we should 1) Point to a physical table if the chart is based off a query or 2) notify the user with a red bang and/or tooltip letting the user know the physical table is missing.

Additional context

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[ericandrewmeadows]

@khtruong - this seems valuable, but costly. This could be a feature that is enabled on a per-database level, because you are issuing a query against the information schema of the given database during this request. What are your thoughts?

[khtruong]

I think in general the experience needs to be improved. If the table is based off a query, then the UI states that the table is the query name. Second, if the table does not exist, then it silently fails. So anything to alleviate the confusion is a step in the right direction.

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