Error toast when creating a monitor for the first time

[ohltyler]

On a fresh cluster, before all of the plugin system indices have been inited, there is an error toast that shows up in the unified flow when creating a monitor with a trigger:

These types of errors should be caught and handled. AD has a solution of filtering out the type of exception being faced, and ignoring if applicable (e.g., loading the detector list page without the .opendistro-anomaly-detectors system index present). See here for details

[ohltyler]

@lezzago can confirm, but this change may need to be backported to versions older than 1.3.

[lezzago]

Fixed in main: #173

@ohltyler to your question, we typically dont backport for older releases, but this can be considered and will leave this open