Advanced task argument default values, optional values, and custom range support

[shreddedbacon]

I'd like to see advanced task arguments improvements to support additional use cases

1. There is no way to define an argument as optional, in the UI I have to populate all fields to be able to trigger the task. If a field is marked as optional, it could skip it.
2. There is no way to define a default value, or values for an argument.
3. STRING_RANGE, and then an input of stringRange: [string] so you could craft your own drop down of predefined options (could do NUMERIC_RANGE too?)

{
	name: "MY_OPTIONAL_VALUE"
	displayName: "Just a value that is optional"
	type: STRING
	optional: true
},
{
	name: "MY_VALUE"
	displayName: "Just a value"
	type: STRING
	default: "value"
},
{
	name: "MY_RANGE_VALUE"
	displayName: "Just a value from a range"
	type: STRING_RANGE
	stringRange: ["value1", "value2"]
}