refs #17714 [master] use inheritance for searchspecs.yaml

* prepare testing directory structure for yaml comparism
** add fixtures in same order as config files
** use symlinks for real configs
** use result searchspecs for old outcome before refactoring
* fix finc test setup for docker
* add finc SearchSpecsReaderTest
** run: docker exec -it [php container] sh -c "vendor/bin/phpunit --configuration module/finc/tests/phpunit.xml module/finc/tests/unit-tests/src/fincTest/Config/SearchSpecsReaderTest.php"
[--filter testParentYaml]"

* in local searchspecs.yaml
** use vufind as parent and keep only delta
* in local alpha searchspecs.yaml
** use local as parent, no delta

* use autoconfig version 2.3.3, see also https://git.sc.uni-leipzig.de/ubl/bdd_dev/webmasterei/autoconfig/-/commit/7b396da68c63820c869d45ca655d70d77b417aef
* add env var for local searchspecs.yaml in docker-env.0.finc.yml