feat: add content_field support to generic_resolver

[mhoff]

Description

• Briefly summarize your changes in a few bullet points (can and should correspond to CHANGELOG.md)
• Relates to #XXX (insert issue number here), if there is a corresponding GH issue

Assignee

• The changes adhere to the contribution guidelines
• I have performed a self-review of my code
• My changes generate no new warnings (e.g. flake8/mypy/pytest/...) other than deprecations

Documentation

• README.md is up-to-date
• CHANGELOG.md is up-to-date
• Documentation (doc/source) is up-to-date
• Preview for docs looks fine
• Notebooks are up-to-date and functional
• Examples are up-to-date and functional (including compose & k8s)

Code Quality

• Patch test coverage > 95% and does not decrease
• New code uses correct & specific type hints

How did you verify that the changes work in practice?

• List of (preferably easy reproducible) tests including OS

Reviewer

• The code is readable/maintainable and follows the contribution guidelines
• Documentation is up-to-date
• Tests (unit & acceptance) are meaningful and not over-mocked

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