Visualize: Bad request when working with histogram aggregation

[flash1293]

Kibana version: 7.10

Describe the bug:

When changing the settings for the histogram aggregation, it's possible to run into a state no interval is provided

Steps to reproduce:

1. Create "histogram" aggregation on X axis
2. Set "Max bars" to 5
3. Apply
4. Remove "Max bars" value to get back to "Auto"
5. Apply
6. "Bad request" error is shown

Expected behavior:
Should use default max bars

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[timroes]

Most likely introduced via #76001

[alexwizp]

@timroes you are right, it's my regression. @dej611 I've created a draft PR (#77684) please review it. Looks like it solve that issue

[flash1293]

@alexwizp I know @dej611 was working on this as well (he's also assigned to the issue). Can you two pair up on this?

[dej611]

Yes, I pushed a fix this morning for it. I'm trying to write a unit test to stop regressions right now.

[alexwizp]

@flash1293 @timroes @lukeelmers
I thought about a good test for this case, but I have doubts about the correctness of the algorithm for calculating the auto interval.

My main concern that for integer numbers it returns float intervals. It's super un-useful. In real example it looks like:

4b2ae64 in this commit algorithm for calculating was changed