feat: projection management API and more comprehensive error strategy

[hseeberger]

So far the initial projection support only offers a minimal ErrorStrategy (stop or retry) and no projection management at all. To be useful in production scenarios, we need:

• add ErrorStrategy::Skip,
• extend ErrorStrategy::Retry with a maximum number of retries, then stop or skip,
• offer a projection management API that allows for
  • stopping a running projection
  • resuming a stopped projection
  • set the sequence number of a stopped projection to any existing value and restart from there