Implements a new AutoConfigurationLoader, which loads
auto-configurations from a file in META-INF/spring-boot.
Adapts the AutoConfigurationImportSelector to use the new loader.
Adapts the ImportAutoConfigurationImportSelector to use the new loader.
Adapts the metadata plugin in the build to additionally load the
auto-configurations from the new file.
Updates the documentation for auto-configurations and test slices.
Closes gh-29872
As described in https://issues.redhat.com/browse/WFLY-15478, Wildfly
25.0.0.Final rejects all requests that use basic auth with a 401
response. 25.0.0.Final is, at the time of writing, the latest available
Wildfly Docker image so we need to downgrade to 24.0.0.Final.
Closes gh-28956
