Feat/add stats for items requests logs objects

[jc99k]

Description

Add stats for objects sent by producer (e.g. to Kafka) that commonly end up as storage:

• item_obj_byte_size
• request_obj_byte_size
• log_obj_byte_size

Checklist before requesting a review

• I have performed a self-review of my code.
• My code follows the style guidelines of this project.
• I have made corresponding changes to the documentation.
• New and existing tests pass locally with my changes.
• If this change is a core feature, I have added thorough tests.
• If this change affects or depends on the behavior of other estela repositories, I have created pull requests with the relevant changes in the affected repositories. Please, refer to our official documentation.
• I understand that my pull request may be closed if it becomes obvious or I did not perform all of the steps above.