How to set default value for route parameter based on configured value? I have a route with optional parameter that has some default value:

# file @hello.routing.yml
hello.sayHi:
  path: '/hello/{name}'
  defaults: 
    _title: 'Say Hi'
    _content: 'Drupal\hello\Controller\SimpleCallback::sayHiAction'
    name: 'there'
  requirements:
    _permission: 'access content'


I'd like to make there value for {name} parameter configurable. Let's assume that this default value for {name} is available in simple config variable.
You must implement a route alter. In the alter code, extract the setting and set the value on the route definition.