Cron trigger for mutations

### Is your proposal related to a problem?

Sometimes I run into a scenario where I have an GraphQL mutation on a remote schema for an action that needs to be run periodically, as well as manually.

### Describe the solution you'd like

Hasura could provide a way to create cron triggers which directly run mutations which are already available through Hasura. Normally these mutations only need static or no arguments.

### Describe alternatives you've considered

An alternative is to create a web hook that calls the mutation and schedule that. Or create a web hook that does the same thing as the mutation. But this web hook would be unnecessary if Hasura could just schedule mutations directly.

The issue names no files, tests, or entry points. Start by identifying the existing cron-trigger and remote-schema mutation entry points; done would mean scheduling already-available mutations with static or no arguments while preserving manual execution.

Written by the indexing model from the issue text.