TDL 17738 sync conversations stream correctly

[prijendev]

Description of change

• Updated logic for conversation stream to overwrite updated_at value by last_edited_at field if it is available.
• If last_edited_at is not None then assign it's value to updated_at field.
• Added unit tests for the changes.

Manual QA steps

• For conversation record with last_edited_at field value, check updated_at is updated.
• For conversation record with last_edited_at field null value, check updated_at is not updated.

Risks

Rollback steps

• revert this branch