proposal: stop storing delegations separately from invocations

[travis]

Context

We currently store delegations in their own R2 bucket. Theoretically, all delegations should also be included in a UCAN invocation that we store as part of the UCAN invocation log, which means that we could just refer to them where they live in the invocations they were originally part of. This was partially implemented in #194.

In practice, delegations created by our access/confirm provider are not included in a UCAN invocation, which means that we cannot complete the work we started in #194 until they are.

Proposal

To finish this work, https://github.com/web3-storage/w3up/blob/main/packages/upload-api/src/access/confirm.js#L59 should be reworked to invoke an access/delegate (? - double check with Irakli) UCAN and then re-enable the FIND_DELEGATIONS_IN_INVOCATIONS feature flag (https://github.com/web3-storage/w3infra/pull/194/files#diff-1fd3717c8177f7e6c62c854a870b4d2fb040f1353302bbacc0edef9bc7bd6ffdR31)