Update the WebDav harvester to support XSLT per schema, similar to the GeoNetwork harvester.

Documentation updates:

• Updated the manual page for the WebDav harvester.
• Added GeoNetwork 2.1-3.x harvester page that was missing and update the harvesters page documentation, that was describing the harvesters page in Geonetwork 2.x.
• Removed the Z39.50 harvester, not available in GeoNetwork 4.x.
• Updated the harvesters main page to describe the harvesters page in GeoNetwork 4.x.

The change request includes also Sonarlint improvements.

Checklist

• I have read the contribution guidelines
• Pull request provided for main branch, backports managed with label
• Good housekeeping of code, cleaning up comments, tests, and documentation
• Clean commit history broken into understandable chucks, avoiding big commits with hundreds of files, cautious of reformatting and whitespace changes
• Clean commit messages, longer verbose messages are encouraged
• API Changes are identified in commit messages
• Testing provided for features or enhancements using automatic tests
• User documentation provided for new features or enhancements in manual
• Build documentation provided for development instructions in README.md files
• Library management using pom.xml dependency management. Update build documentation with intended library use and library tutorials or documentation

Funded by: Rijkswaterstaat