Persist access & refresh token in trigger service

The trigger service persists running triggers in a database. We should store access and refresh tokens for triggers in this database when authentication/authorization is required. See [here](https://github.com/digital-asset/daml/blob/0b1adc8e2e9d1b4d7828d6b222879ebaabd6947a/triggers/service/src/main/scala/com/digitalasset/daml/lf/engine/trigger/dao/DbTriggerDao.scala#L146).

Part of #6923.