[Settings migration] Track total insights on an instance, by type if possible.

Created by: Joelkw

Track total insights on an instance, by type if possible.

We don't seem to have this and it's hard to do via settings files.

We have long ago gotten RFC/bizops approval for this.

Something of the form:

{
"codeStatsInsights":3,
"searchBasedInsights":81,
"searchBasedExtensionInsights":26,
"searchBasedBackendInsights":55
}

is perfect. It can just reflect total of all time (we can subtract to get differences week to week).