Add AutoGTPSA backend

[mattsignorelli]

Checklist

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

Additional context

This PR adds the AutoGTPSA type for choosing the GTPSA.jl backend. Bindings to DifferentiationInterface.jl are ready here

[gdalle]

Thank you for this addition! Let me just review https://github.com/gdalle/DifferentiationInterface.jl/pull/329 first to make sure we're not missing anything in the backend object