Color mapping feature case-sensitivity

[cachedout]

Kibana version:
8.12.0
Elasticsearch version:
8.12.0
Server OS version:
ESS
Browser version:
Brave
Browser OS version:
Mac OSX
Original install method (e.g. download page, yum, from source, etc.):
ESS deployment
Describe the bug:
In the case where you have two separate fields where they are only distinguished by case, the Color Mapping picker refuses to let you select the two cases. A screenshot below demonstrates this in action. Not the lack of an option for Strongly Disagree in the Color Mapping picker, despite it being shown in the chart to the left.

Steps to reproduce:

1. Create ES documents with two fields which are only distinguished by case.
2. Attempt to create a visualization and use the Color Mapping feature to associate colors with the two fields.
3. Note that only one field can be chosen.

Expected behavior:
See reproduction steps.
Screenshots (if relevant):
See in-line screenshot.
Errors in browser console (if relevant):

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

Any additional context:

[elasticmachine]

Pinging @elastic/kibana-visualizations (Team:Visualizations)

[stratoula]

cc @markov00

[markov00]

I have a fix for this here #175144 but even though I see how this is a logic issue in the code, I strongly believe that such a case should not be fixed here in the color mapping, instead, this should be fixed in the data itself (in the ingestion pipeline or a cleaning/preparation phase).
The reasons: if two terms only differ by their letter case, 99.9% of the time those two terms are semantically the same and they should be "aggregated" together. You can always color the two slices the same way, but their values are not summed together and an interaction over the chart can cause confusion and misinterpretation.