[Feature] Autocomplete drop down first phase

[KatiePUX]

Default drop down with action e.g. 'search organisation' as default as recommended via GDS;
https://alphagov.github.io/accessible-autocomplete/examples/

User clicks inside dropdown, focus state appears, results appear alphabetically

When a user begins to type list adjusts alphabetically
When list exceeds 5, list to be scrollable, with a limited view of 5

When a user hovers over an item

When a user enters an incorrect value

When a user enters an incorrect value and clicks outside of the input field