bug: add handler for handling changed domain

[carlinmack]

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(Part of) Close inveniosoftware/invenio-app-rdm#2777

Description

Please describe briefly your pull request.

We call mark_changed but we did not check that it handled Domains

Calling flush as similarly done in the pre-commit hook

Also remove setting of role.id as the added flush() will add the ID from DB

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[lnielsen]

@slint Can you have a look at the impact of having a flush here.

[slint]

I see we very often tiptoe around flushes, and get them in implicitly just by chance because we perform another SELECT query down the line, e.g.:

domain = Domain.create(...)

# ...in another function...

user = UserAggregate.get(...)  # <-- this triggered a flush, so our `domain`
                               #     from above now has a `domain.id`

So I think it's better to be explicit about it, which is what calling mark_changed also implies (i.e. that something will be persisted to the DB).

@carlinmack is also checking this change on tests across other repos to see if there are wrong expectations.