Feature: #88742 - Import Yaml files relative to the current yaml file

See Issue #88742

Description

The configuration language YAML (Yet Another Markup Language) is used to configure rich-text editor configuration, Form Framework form definitions, and site handling configuration files.

TYPO3’s internal YAML loader has a special handling for cascading and including other YAML files into the loaded resource via the following syntax:

imports:
  - { resource: "EXT:rte_ckeditor/Configuration/RTE/Processing.yaml" }

another:
  option: true

However, the reference to the file was usually handled by referencing other resources in extensions as in EXT:my_extension/Configuration/MyConfig.yaml.

This is now optimized to allow imported resources to include files relative to the current YAML file:

imports:
  - { resource: "misc/my_options.yaml" }
  - { resource: "../path/to/something/within/the/project-folder/generic.yaml" }

another:
  option: true

Impact

Especially when using advanced site handling with multiple sites and similar configuration, it is now possible to have one base configuration file that is referenced by the specific site configuration files allowing to keep common config in a single place.