feat(htmlvalidate)!: use `StaticConfigLoader` by default
BREAKING CHANGE: This change only affects API users, the CLI tool continues to work as before. The default configuration loader has changed from `FileSystemConfigLoader` to `StaticConfigLoader`, i.e. the directory traversal looking for `.htmlvalidate.json` configuration files must now be explicitly enabled. See (MIGRATION.md)[https://html-validate.org/migration/index.html] for details.