Support setting `maxItemsDisplayed` for `RplFormDropdown` in webform mapping or feature flag

[bgilhome-now]

Describe the feature

The default value for maxItemsDisplayed in RplFormDropdown is 6, which for lists with a large number of options can mean a lot of scrolling. It might be convenient to add a feature flag to set the default number of items, or support setting 'maxItemsDisplayed' via "Advanced -> Element attributes -> YAML" in the Webform build UI for a field.

Motivation

Improve UX

Proposal

Add either or both of:

1. a feature flag to set default maxItemsDisplayed for RplFormDropdown
2. mapping of maxItemsDisplayed or some other property name in element attributes in ripple-tide-webform's mapping for the 'select' case

Benefits

For dropdowns with more than 5 options, alleviating the need to scroll, and making it clear to the user the additional options.

Drawbacks

Developers/form editors might set an unusably large value - this could be capped to a sane maximum.

Adoption strategy

Docs/story

Additional information

• Would you be willing to help implement this feature?
• Could this feature be created outside of Ripple-framework as a layer?

Final checks

• I have read the contribution guide for information on submitting a feature request.
• I have checked the discussions and issues for duplicate feature requests.

[dylankelly]

@bgilhome-now thanks for the submission, makes sense. Do you have an example in the wild that particularly illustrates the issue to help me make the case?

[bgilhome-now]

Thanks @dylankelly - the EPA Permissions register page (http://epa.vic.gov.au/public-registers?register=permissions) has some long dropdowns - however NB the Activity & Waste Code fields will be getting 'search enabled' set soon which will help UX there.