TSVB Visual Builder test automation meta issue

[LeeDr]

Describe the feature: Automate additional tests for TSVB "Visual Builder"

Describe a specific use case for the feature:
Since we haven't selected a visual regression testing tool yet, it might be easiest to Data Table or Markdown parts of TSVB to verify the results of different aggregations and metrics.

We can use the open github issues on tsvb to help find good test cases and also discuss posts.
May also want to check closed/fixed github issues to find problem areas to add tests for.

We should start another test file in the visualize folder so that this test file doesn't get too large;
https://github.com/elastic/kibana/blob/master/test/functional/apps/visualize/_tsvb_chart.js

I think we need to add cases for multiple metrics, many types of aggregations, and other options not currently tested. But we need to check on what unit tests exist or are possible to add before doing too much UI automation.

https://www.elastic.co/guide/en/kibana/current/time-series-visual-builder.html

https://www.elastic.co/blog/master-time-with-kibanas-new-time-series-visual-builder

• Here's an example of a Calculation aggregation that might be a good case to automate if we can get the results to show in the Data Table tab; https://discuss.elastic.co/t/scripted-field-with-division-does-not-show-result/97246/8?u=leedr

• another possible case; https://discuss.elastic.co/t/doing-math-over-count-of-events/97278/33

[vitalics]

add new markdown tests in #30642
reference #23418

[vitalics]

actual reference #31893
backport this tests to 7.x version: #32471

[vitalics]

new TSVB markdown tests. These tests are includes variables and label changing: #33324
reverted tests #34067

[vitalics]

TSVB table tests #35162

[timroes]

Since we've added a couple of more TSVB automation tests (as linked in this issue), I am going to close this.