Fix TODOs

[fristonio]

Fix all the TODOs we have. git grep "TODO"

core/auth/token.go:// TODO: change this from username to email.
core/manager/challenge.go:      // TODO: Later replace this with a manifest file, containing Information about the
core/manager/challenge.go:              /// TODO : remove multiple validation while deploying challenge
core/manager/challenge.go:      // TODO: Why are we creating tag entry here, if there does not
core/manager/challenge.go:                      //TODO : challenge transaction save for deploying is not done since ID is not provided here
core/manager/utils.go:// TODO: Refactor this.
core/manager/utils.go:  // TODO: Do all this under a database transaction so that if any port
pkg/workerpool/pool.go: // TODO : get size of the queue