This commit introduces the multi-layer time axis in Discover, Lens, Visualize, TSVB.
It adds visualization:useLegacyTimeAxis advanced settings under charts plugin to toggle legacy time axis.
The new multi-layer time axis is introduced in @elastic/charts https://elastic.github.io/elastic-charts/?path=/story/area-chart--timeslip and was demoed as part of the Kibana Demo Days.
It is the outcome of the research done in elastic/elastic-charts#1310 related to improving the time axis solving the following problems:
- sparse time labels that can be far apart
- unclear where time point is on the label (the middle)
- difficult / tedious to read due to redundant information and small fonts
- resolution is not explicit (is it hours of days or days themselves)
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