merge wendelin.git to erp5.git

After discussion of https://lab.nexedi.com/nexedi/slapos/-/merge_requests/1822#note_239092, it seems we need to move wendelin.git to erp5.git to be more consistent

Related MRs: https://lab.nexedi.com/nexedi/slapos/-/merge_requests/1859, https://lab.nexedi.com/nexedi/wendelin/-/merge_requests/183

here are the changes for

wendelin.git:

1. wendelin/bt5/* is moved to erp5/bt5/*, with commit history

2. wendelin/tutorial, wendelin/utils, wendelin/CHANGES.md, wendelin/README.md are moved to erp5/wendelin with commit history

3. wendelin/product/Wendelin/__init__.py is merged to erp5/product/ERP5Type/patches/Restricted.py

4. wendelin/scalability_test/example is moved to erp5/scalability_test/example_wendelin with commit history

5. wendelin/scalability_test/cluster_configuration_template.json is moved to erp5/scalability_test/cluster_configuration_template_wendelin.json with commit history

6. wendelin/scalability_test/__init__.py is merged to erp5/scalability_test/__init__.py

7. wendelin/tests/__init__.py is merged to erp5/tests/__init__.py

others files are dropped

erp5.git:

Beside the changes of above, testGC is adjusted, please check https://lab.nexedi.com/nexedi/erp5/-/merge_requests/2117#note_238776 for more informations