From linkml to schemapack

[sbilge]

This PR includes scripts and files to convert ghga-metadata-model from its LinkML representation to SchemaPack definition.
The bash script migrate_to_schemapack.sh calls the scripts in the required order and cleans up the repository from LinkML-related files and folders.

[dontseyit]

I looks good to me, I'm not able to review schemapack logic at the moment but I suggest some improvements to the code.

[sbilge]

I updated the branch based on the ghga-metadata-schema (on linkml) changes. I introduced a new condition to extract_relationships.py script to prevent the script from interpreting two specific fields as a relationship. The explanation is also provided in the function definition of slots_with_class_range. The scripts extract_class_content.py, extract_relationships.py, and linkml_to_schemapack.py will not live on the repository and they are only included in this PR for archiving purposes. After getting approval on the migration strategy, I will once more clean up the repository.