detected schema is never updated and becomes stale

[mschoch]

The plugin retrieves the schema once on initial page load, but it never updates after that.

I often leave grafana tabs open for a long time, and a few times now I notice that the detected schema is stale (fields or dataset name with underline, but query executes correctly). A force refresh of the whole page resolves the problem, but it feels like even a simple periodic refresh (say ever 15min) would hide the problem for most users.