Make the "info" field mandatory in the taskprov configuration method for `DapTaskConfig`

[cjpatton]

This is optional because in the past we have stored task configs in KV that were configured by taskprov but lacked the "info" field needed to reconstruct the taskprov advertisement. We should be able to safely drop this, but there may be side-effects and we need to make sure to monitor deployment.

Originally posted by @mendess in https://github.com/cloudflare/daphne/pull/541#discussion_r1530272076