Implement git init

Allows creation of new git repo, may be of use in tests.

infrastructure_api.py

@@ -212,6 +212,9 @@ class GitApi():
         self.system_repository.run_checked('git', 'branch', '--show-current')
         return ''.join(self.system_repository.stdout).rstrip()
 
+    def init(self):
+        self.system_repository.run_checked('git', 'init')
+
     def add_file(self, file_path: Path):
         self.system_repository.run_checked('git', 'add', file_path)
         return self.system_repository.stdout