[TSVB] "Bounds Band" mode broken on both Std. Deviation and Overall Std Deviation

[simianhacker]

Kibana version:
7.7 BC5

Elasticsearch version:
7.7 BC5

Original install method (e.g. download page, yum, from source, etc.):
From downloaded archives

Describe the bug:
When using the "bounds band" mode on both the Std. Deviation and Overall Std. Deviation aggregations.

Steps to reproduce:

1. Run Metricbeat locally and send data to Elasticsearch
2. Create new TSVB visualization
3. Set Aggregation to Std. Deviation
4. Set Field to system.cpu.user.pct
5. Set Mode to Bounds Band
6. Screen should look like screen shot below

Expected behavior:
Should display a shaded area between the upper and lower bounds

Screenshots (if relevant):

Errors in browser console (if relevant):

[elasticmachine]

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

[timroes]

cc @sulemanof This looks similar to #58840 but seems to be caused by a different root cause, since not fixed by your fix. Do you want to have a look at this one?