Add post dump hooks

- Allow for a custom command to be run after something is dumped
- This could (for example) attempt to remove rows with a deleted field set

You should be able to define formats the hooks are called on.

Potential config:

```yaml
hooks:
- type: post_dump
format: sql
command: /path/to/runnable/file
```

The issue proposes configurable post_dump hooks, including a command and the formats on which each hook runs. Define what supported hook behavior and completion criteria are before locating the relevant configuration and dump-processing entry points; done means a configured command runs after the selected dump format is generated.

Written by the indexing model from the issue text.