Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

This is an initial attempt to support DifferentiationInterface.jl as a backend for computing derivatives of user integrands. Users still have to pick a differentiation package with a rules system supported by Integrals.jl. Will close #258 when completed.

This pr is in a draft status mainly so I can see the results of CI without running all derivative tests locally. So far I have only checked that 1d scalar oop integrands work, but there are more goals for this pr:

• Add a forward-mode rule
• Support more rules systems (currently ChainRules, but eventually EnzymeRules)
• Try supporting derivatives of multi-dimensional limits (i.e. just implement the Leibniz rule)