Summary: as discussed with malthus, the types directory is the best place to keep this code. i put it into a "generated" directory so that excluding it from lint is easier

Test Plan: n/a... need to write an arc unit test to make sure these files are regenerated

Reviewers: zasgar, malthus, #engineering

Reviewed By: zasgar, #engineering

Differential Revision: https://phab.corp.pixielabs.ai/D3579

GitOrigin-RevId: 45dc28a54c087c5bbcdedbacc348006c09f3c318