Add multi-select, proposals and labels for trigger form

[jscheffl]

closes: #31440
related: #31301 #31399

This PR adds three new (small) features into the Trigger DAG UI form for increased usability and new (missing) features:

• In select lists (rendered via enum) display labels can be added to separate picked value and display text in dropdown via values_display property.
• If user should have proposals for entering values but should not be forced to the limited number of enums now the attribute examplescan be used which are used to present proposals while typing
• Multi-value selects are now possible (So that not only enums with single values need to be used). These are a combination of array type and examples.

Tutorial is adjusted with examples for the new features, UI looks like this for the three new options:

This PR overlaps a bit with https://github.com/apache/airflow/31400 so the other should be merged first and then this needs to be adjusted.

[pierrejeambrun]

Overall looking good. :)

I just have an issue with multiselect field:

• Select multiple value in the Multi Select *:
• Submit the run
• Try to trigger again this dag using previous configuration we made for the 1st run
• The field is not properly populated. It uses the default value for the param, while we are using the previous configuration. The Generated Configuration JSON though is correct (with values from the former run)

[jscheffl]

Overall looking good. :)

I just have an issue with multiselect field:

* Select multiple value in the `Multi Select *:`

* Submit the run

* Try to trigger again this dag using previous configuration we made for the 1st run

* The field is not properly populated. It uses the default value for the param, while we are using the previous configuration. The `Generated Configuration JSON` though is correct (with values from the former run)

You found a generic bug before this PR actually - never have seen this before. Thanks for finding. Select boxes anyway were not correctly re-populated with data when recent config was selected. Fixed now. (Detail: Just setting the value property is not sufficient, the select2 boxes need a specific call to set the data :-(

[jscheffl]

closes: #31869