Update IPA and Hybrid repos

[bmcase]

Does it make sense to checkpoint the IPA v2 branch under private-attribution/ipa while moving the hybrid branch to private-attribution/hybrid? Could help make is easier to understand what the code is implementing in each case.

[akoshelev]

We could be more explicit about what version resides in the main branch. Main branch is default by convention, so we may not want to change it.

So far we have oprf-ipa and ipa-v2 which is probably confusing. We could rename oprf-ipa to ipa and ipa-v2 to legacy-ipa or something similar, if that helps