Improve support for asynchronous questions

[cortadocodes]

Feature request

Use Case

We'd like to be able to "fire-and-forget" a question and then retrieve its events (including results) separately later.

Current state

Questions can be asked:

• Synchronously
• Asynchronously (but their results and events can't be easily retrieved)

Proposed Solution

• Adapt Service.ask to work with BigQuery subscriptions
• Provide convenient asynchronous method or argument in Child class
• Test sending events to BigQuery via a push subscription
• Add a function to retrieve an async question's events with:
  • Any combination of the following:
    • Inputs
      • Remove sender_type part of filter in bigquery answer subscriptions
    • Output values and manifest
    • Output datasets
    • Log messages
    • Monitor messages
  • Output format options:
    • JSON
    • Just events
    • Events and attributes
    • Events attributes, and Pub/Sub metadata
• Add a CLI command that does the same (not needed for MVP)
• Add a function that replays events retrieved asynchronously
  • Returns result
  • Optional replay of logs etc
  • Remove need to provide SRUID of child when replaying (see Add/update attributes in event schema #634)
• Decide whether bigquery tables should be specified per question (by the parent) or per child (by the child)
  • If bigquery tables are specified per question, automatically delete BigQuery subscriptions once their result event has been received and stored
• Set up bigquery table for project
• Update documentation including adding an info box warning that an event store (e.g. BigQuery) needs to be set up for events from asynchronous questions to be usable