Fix the schema artifact name in add schema script

[josegar74]

Maven artifact identifiers were changed to include the gn- prefix, the script for adding metadata schemas to the development project was not updated.

This change requires revising the custom schemas at https://github.com/metadata101 to use the old convention if they are not already using it.

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