Expand available modes

[unix196]

New values can take from there:

SELECT * FROM system.metrics

From this table interesting especially Query, Merge, BackgroundPoolTask.
(in our case our cluster went into degradation mode when BackgroundPoolTask increased from ~0.35 to 16)
Example graphic - https://ibb.co/Qrjk0Nr

[lisuml]

I will try looking into it soon. Thanks.