Entity Name Picker
Overview
This picker is introduced to set a default variable for your input field (usually you want this to be the name input field).
Configuration
Along with that, as some pickers already do, you can define ui:options: allowArbitraryValues: false to block the user input on that field. Furthermore it's possible to define maxLength to limit the number of characters. The whole picker definition (inside template.yaml) would look something like this:
name:
title: Name
type: string
ui:field: EntityNamePicker
default: <your_default_value_goes_here>
ui:options:
allowArbitraryValues: false
maxLength: 20