Deduplicate module version creation code

Each of the module version upload API endpoints contain something similar to:

                    previous_version_published = module_version.prepare_module()
                    with terrareg.module_extractor.GitModuleExtractor(module_version=module_version) as me:
                        me.process_upload()

                    if previous_version_published:
                        module_version.publish()

This should be deduplicated into a function. There is no interaction between the ModuleVersion model and the Extraction classes - should the functionality be within the extractor methods?