added urlDNA.io observable analyzers documentation

[redaelli]

Documentation for PR: <added urlDNA.io observable analyzers>. PR #2580

Checklist

• The pull request is for the branch main
• If I added new documentation related to a new Pull Request that I created, I have added a reference to the related Pull Request
  • If the new documentation will be added in a future release, please add a reference like _Available from version > x.x.x_ where x.x.x is the current version number
• If the additional documentation is a fix, you should directly push to the main branch and do not open this PR.