Purge documents

[sandreae]

📋 Checklist

• [ ] Add tests that cover your changes
• [ ] Add this PR to the Unreleased section in CHANGELOG.md
• [ ] Link this PR to any issues it closes
• [ ] New files contain a SPDX license header

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (ffc1b74) 92.18% compared to head (ffc1b74) 92.18%.

:exclamation: Current head ffc1b74 differs from pull request most recent head b26b722. Consider uploading reports for the commit b26b722 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## development #499 +/- ## ============================================ Coverage 92.18% 92.18% ============================================ Files 102 102 Lines 16644 16644 ============================================ Hits 15344 15344 Misses 1300 1300 ```

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[sandreae]

Closing this PR in favour of implementing this logic together with "pruning" documents in a single "garbage_collection" task: continued in https://github.com/p2panda/aquadoggo/pull/500