NIFI-6323 Changed URLs for splunk.artifactoryonline.com to use HTTPS (certificate validity warning in browsers, but command-line connection using openssl s_client is successful).
NIFI-6323 Changed URLs for XMLNS schema locations to use HTTPS (the XMLNS and schema identifier remain http:// because they are not designed to be resolvable).
NIFI-6323 Fixed Maven XML schema descriptor URLs.
This closes#3497