Add new helper for ListProcessElements

This helper should be a method in a new mixin named ProcessMixin in arkindex_worker.worker.process.

Parameters of the method are:

• with_image: bool, defaults to False

Port:

• INIT_PAGE_SIZE and use it as page_size for this endpoint
• allow_missing_data=True, to allow failure on some pages, for large dataset (refs https://gitlab.teklia.com/arkindex/api-client/-/blob/8b1f966c35158271cd7214f79d90cf8393ffdc61/docs/usage.md#L67)

This method doesn't support cache.

Refs https://redmine.teklia.com/issues/7497