Fix modal dialogs with large contents

[gjvoosten]

Make sure modal dialogs with (potentially) large contents, like assessments or related object notes, scroll properly.

Closes AB#889

User changes

• Modal dialogs with large contents now scroll properly if the contents don't fit on the screen.

Superuser changes

• None

Admin changes

• None

System admin changes

• anet.yml or anet-dictionary.yml needs change
• db needs migration
• documentation has changed
• graphql schema has changed

Checklist

• Described the user behavior in PR body
• Referenced/updated all related issues
• commits follow a repo#issue: Title title format and these 7 rules
• commits have a clean history, otherwise PR may be squash-merged
• Added and/or updated unit tests
• Added and/or updated e2e tests
• Added and/or updated data migrations
• Updated documentation
• Resolved all build errors and warnings
• Opened debt issues for anything not resolved here