Add support for the TestExpectation model field `MayInclude` (which maps to the yaml `output_contains_any` field.

[LarryOsterman]

There are several places in the tree which reference this field:

docs/GETTING-STARTED.md
examples/code-explainer/tasks/explain-js-async.yaml
examples/code-explainer/tasks/explain-list-comprehension.yaml
examples/code-explainer/tasks/explain-python-recursion.yaml
examples/code-explainer/tasks/explain-sql-join.yaml
site/src/content/docs/getting-started.mdx
site/src/content/docs/guides/eval-yaml.mdx
site/src/content/docs/reference/schema.mdx

expected:
  output_contains:
    - "list"
  output_contains_any:
    - "square"
    - "x**2"
    - "power"
    - "comprehension"

Unfortunately, while there is support for the mandatory MustInclude (output_contains) field, there is no support for the MayInclude field, which defines a set of words some of which must appear in the output.

It seems that a "MayInclude" style field (a set of words where some number of them must appear, but not ALL of them) is a useful construct so it should be added.