* tests: add test case for FileDigestGroup with multiple package names
* FileDigestCheck: support additional `packages = ["pkg1", "pkg2"]` syntax
* FileDigestCheck: refactor digest group parsing and normalization
* FileMetadataCheck: support additional `packages = ["pkg1", "pkg2"]` syntax
OBS-URL: https://build.opensuse.org/package/show/devel:openSUSE:Factory:rpmlint/rpmlint?expand=0&rev=865