Extra long index names prevent Time Field from being selected when creating Index Threshold Alert

[jeffvestal]

Kibana version:
7.7

Elasticsearch version:
7.7

Browser version:
Chrome 83

Browser OS version:
Mac

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

Describe the bug:
In the Alert UI fly out (from the management section) when you select a very log index name or pattern for the index source the "Indices to query" box blocks the "Time Field" selector. Barrier seems to be around 67 characters.

This came up when I was selecting a ML anomalies index as the source. The index was auto named and created when I created a "categories" ML job through the Logs UI.

Steps to reproduce:

1. Create a new Index threshold Alert
2. Select a very log index name or pattern
3. Time field picker box will be pushed off screen as you type and when you select an index the time piker box will not be visible or selectable

Expected behavior:
I would expect either the time picker to be pushed to the next row, or the index name to be truncated. Somehow allowing the time field to be selected.

Screenshots (if relevant):
Anomaly index pattern chosen and the Time Picker box is no longer on screen

Clicking out of the selector shows the error of no time field,

Here you can see the time field being pushed off screen

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context:
Most indices will not be this long, but since this was an index auto created from the Logs UI / ML integration I could see some users running across this issue when trying to create ML alerts with the new Alerting framework until an actual workflow is created.

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[mdefazio]

Here are some initial thoughts on fixing this.
If we show truncated within the form and combo box, we can avoid breaking layout changes. And would then show the full index (or other value) name via tooltip.
We could also switch the forms within the popover to be compressed and hopefully minimize the amount of case where this happens.

[pmuellr]

looks good to me!

[andreadelrio]

I can take care of this one