tasks: define RFC for persistence

Placeholder ticket for defining "Task Persistence".

- We want to be able to persist task logs (input + output from the application running the task).
- These logs contain important context for the user and should remain accessible after the task is completed.
- We additionally want to be able to detect artefacts created by tasks and allow template authors to define ways to automatically persist said artefacts.
- An example of an artefact is edits to preexisting source code, or new additions to source code.
- An example of a persistence method is committing and pushing to a new Git branch.