[ML] Single Metric Viewer combobox does not provide all possible values

[timsn]

Kibana version: 7.4

Elasticsearch version: 7.4

Server OS version: RHEL 7

Browser version: Firefox 60.8.0esr (64bit)

Browser OS version: RHEL 7 MATE Desktop

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

Describe the bug: In the Single Metric Viewer tab of the Machine Learning feature page (X-Pack) the combobox for selecting a detector value does not contain all possible values. Only a limited subset of values seems to be available.

Steps to reproduce:

1. Open kibana and go to "Machine Learning"
2. Create a ML job (in this case multi metric) using a partition_field with many distinct values (e.g. more than 250.000)
3. Open the ML job and go to the "Single Metric Viewer" tab
4. Besides the "Detector" field open the combobox to select a value (see screenshot) and note that not all of the possible values can be found in this list.

Expected behavior:
The combobox should contain all of the available values to select from

Screenshots (if relevant):

Errors in browser console (if relevant):

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

Any additional context:

[sophiec20]

Related: #52541

I believe that only TSID.keyword values that contain anomalies will be able to be viewed with this version.

In the case above, it would not be advised to use model plot for that many values as cardinality is very high.

[elasticmachine]

Pinging @elastic/ml-ui (:ml)