vmui: metric explorer doesn't set properly the default step value

[valyala]

Describe the bug

Navigate to https://play.victoriametrics.com/select/accounting/1/6a716b0f-38bc-4856-90ce-448fd713e3fe/prometheus/graph/#/metrics and try opening a graph for some metric.

To Reproduce

The graph returns "step"=0ms is out of allowed range [0 ... 3153600000000] error.

Expected behavior

The default step value must be automatically calculated for the selected time range and the graph should be properly opened.

Possible workaround

To switch to Custom panel tab and then to switch back to Explore metrics tab. After this graphs are opened as expected.

Additional details

Related issue - #3386

[valyala]

The related bug has been discovered - the graph returns too many points for the given start=..., end=... and step=4000: ...; the maximum number of points is 30000; error when selecting big time range (for example, the last 30 days). This points to incorrect calculation of the automatically set step value. Probably, this is related to the fix for #3513 at #3521

[valyala]

The bug has been fixed by #3561 . Closing the issue then, since the bugs described here weren't included into VictoriaMetrics releases.