Distribution emails -- on change, if you add items, they do not show up in the email, and if you *only* add items, no email is generated (i.e. if you don't change levels of existing items)

Summary

The email sent out on distribution changes is not handling some changes correctly. Fix it.

Why?

Could be misleading

Details

To see the problems:

Using your local copy of the application:
sign in as org_Admin1@example.com
click on Distributions
choose an editable distribution (it's possible you may need to enter a new one) Note the partner for that distribution
Next, Confirm that that partner receives distribution notices:

• click on Partner Agencies, then All Partners
• Click on the partner name
• Click on "Edit Partner Information"
• Ensure that the "Do you want this partner to receive emails..." checkbox is checked, and then click "Update Partner".
  Go back to the distribution
  click Edit

Problem 1/
Change the level of one of the items, and add an item
Click Save

You will see that the email that comes out includes the updated item but not the added item.

The email should include a line detailing the added item.

Problem 2/
Same thing, but add an item without changing any items.

No email is sent. An email should be sent regarding the added item.

Criteria for completion

• behaviour changes as detailed above
• tests that confirm those behaviour changes
• no user guide update is required

Please note:

• there is a separate issue regarding the awkward wording of the text in the email

Start with the Distributions edit and Save flow described in the issue, then trace how distribution-change emails are generated. Reproduce both cases locally using the listed partner and distribution steps, and locate the existing tests covering distribution notices. Done means added items appear in emails and adding items alone sends an email, with tests confirming both behaviors.