util: Improve documentation and negation of args

• Document -color as only applying to -getinfo, to be less confusing for bitcoin-cli users.
• No longer print version information when getting passed -noversion.
• Disallow -nodatadir as we cannot run without one. It was previously interpreted as a mix of unset and as a relative path of "0".
• Support -norpccookiefile
• Support -nopid
• Properly support -noconf (instead of working by accident). Also detect when directories are specified instead of files.

Prompted by investigation in https://github.com/bitcoin/bitcoin/pull/16545#pullrequestreview-2316714013.