Add a diagnostic screen in the UI to notify of major errors #3094
Description
Often quickwit does not work due to some obvious problem: unable to connect to metastore, no control plane, lack of indexer,
impossibility to connect to the storage, etc.
We usually log those errors properly... But these logs are sometimes hidden in a sea of logs and users are not always looking at them.
It could be useful to report those major errors in the UI, on a diagnostic screen, showing clearly what is working (source connectivity, etc.) and what is not.