Do not mark all properties of a map as required

[yngvark]

Description

From app-v8.3.2.schema.json:

    "AlbHostRouting": {

      "required": [
        "Internal",
        "TargetGroupTargetStickiness",
        "Enable"
      ]

TargetGroupTargetStickiness is not actually required, the app template supports it not being specified.

Motivation

IntelliJ makes my app config yellow and ugly. As a YAML editor that likes order, I don't want to put all possible attributes in my app YAML. I.e., I don't want to put TargetGroupTargetStickiness here, I want less clutter.