Turn curation providers into plugins #6056
Description
Similar to e.g. advisors and scanners, package curation providers should become ("named") plugins (discovered by ServiceLoader). This would enable third parties to write custom curation providers without modifying ORT, like curation providers that "calculate" curations based on package properties, or implement other feature like wildcards that ORT core currently does not support.
The implementation of this relates to #6055.