PAPI allowing a user plugin to load its config files

User plugins historically load configuration files via the internal API ctx.artifactoryHome.haAwareEtcDir. This API is no longer available as of Artifactory 7, and something new needs to be used instead. Since configuration files are so integral to the design of most plugins, it makes sense to add explicit support for them to the PAPI, rather than incorporating another hack using the internal API.