Move self-holding logic from core to Sim2h to fix consistency model problems

[lucksus]

PR summary

These changes replace merging the authoring list into the gossip list with code in sim2h_worker that makes the instance hold everything it's authoring.

This has two benefits:

1. Always merging the authoring into the gossip list was the only code in core that assumes a full-sync DHT. We don't want that assumption in core - if we are in a full-sync or sharded DHT should be only sim2h's concern.
2. By having core hold it's own entries explicitly we are true to the assumption in Hachiko - namely that we can tell by the core action HoldAspect if a node is holding something.

testing/benchmarking notes

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followups

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changelog

• if this is a code change that effects some consumer (e.g. zome developers) of holochain core, then it has been added to our between-release changelog with the format

- summary of change [PR#1234](https://github.com/holochain/holochain-rust/pull/1234)

documentation

• this code has been documented according to our docs checklist