Uniquely identify assessments in the dictionary by key

[gjvoosten]

Assessments in the dictionary had no key, which meant at most one definition for each recurrence type was possible. Now they have a key that uniquely identifies them, which in future would allow multiple assessment definitions with the same recurrence, e.g. several ondemand assessments.

Closes AB#296

User changes

• None

Super User changes

• None

Admin changes

• None

System admin changes

• anet.yml or anet-dictionary.yml needs change
  If the dictionary previously contained e.g.:

  fields:
    task:
      subLevel:
        assessments:
          - recurrence: monthly
            questions:
              …
  

  this must now become:

  fields:
    task:
      subLevel:
        assessments:
          subTaskMonthly:
            recurrence: monthly
            questions:
              …
  

  Carefully update all assessment definitions, and give each a unique (and meaningful) key.
• 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