Replace the URLs for the enum files to absolute local path when running AMDirT validate locally

[alexhbnr]

Currently, AMDirT validate pulls the enums containing the allowed values from GitHub. According to @maxibor, GitHub restricts the number of requests when trying to access the files. A work around could be to add a flag, e.g. --local that replaces the GitHub URLs with the absolute paths to the local files because the JSONschema library doesn't allow for relative paths.