code: def init_app(self, app):
          '''
          Initialize this Flask extension for given app.
          '''
          self.app = app
          if not hasattr(app, 'extensions'):
              app.extensions = {}
          app.extensions['plugin_manager'] = self
          self.reload(f init_app(self, app):
          '''
          Initialize this Flask extension for given app.
          '''
          self.app = app
          if not hasattr(app, 'extensions'):
              app.extensions = {}
          app.extensions['plugin_manager'] = self
          self.reload()
docs: Initialize this Flask extension for given app.