[feature] Add a new processor plugin for "whois" information

Now that #1941 makes everything cleaner, we can go back to solving pluggable 'processors', a new one could be "whois" plugin

https://github.com/richardpenman/whois

this would just take the domain-name from the URL and pass it to the whois-processor, probably these should live as separate pypi packages

`changedetectionio-whois` or something could be nice

Start by reading issue #1941 to understand the proposed pluggable processor structure, then review the linked Python whois package. Define how the URL’s domain name reaches a whois processor and whether the processor belongs in a separate PyPI package such as changedetectionio-whois. Done means the plugin boundary and packaging approach are established and the processor can receive domain names.

Written by the indexing model from the issue text.