Add diff for many associations without primary keys

[ddidwyll]

trafficstars

Hi, I actively use ecto_diff in my projects, and sometimes I miss the ability to diff on embeds_many associations without a primary key. I propose a patch to add this feature.

[sourcelevel-bot[bot]]

Hello, @ddidwyll! This is your first Pull Request that will be reviewed by SourceLevel, an automatic Code Review service. It will leave comments on this diff with potential issues and style violations found in the code as you push new commits. You can also see all the issues found on this Pull Request on its review page. Please check our documentation for more information.

[vanvoljg]

Hello! Thank you for the PR! :tada:

It would be fantastic if you could include a test for this feature. Is that possible?

[ddidwyll]

Yes, of course, I'll write tests a little later.

[ddidwyll]

I wrote a small test that shows how this feature can work.

[vanvoljg]

Hello! Sorry about the delay in getting back to you. Too many GitHub notifications. I'll take a look at these changes shortly!