Don't use AcceptQueue for State subnetwork

[morph-dev]

Using AcceptQueue for State network doesn't work because we can't verify content received that way.

We should either:

1. accept multiple Offers for the same content in at the same time
   • we might want to limit how many of these we want to process in parallel
   • downside: we potentially receive the same content multiple times
2. use AcceptQueue but don't ask for the content from fallback peers

I think we should do the first one, but we can refactor AcceptQueue to support this use case. For example, it would be configurable how many entries are "ongoing" and how many are "fallback" and different subnetworks can configure it differently.

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Background: #856 (fixed with #1209)

When we receive Offer for content key from a node A, we put it in the AcceptQueue.

If another Offer request comes from other peer (node B), we will reject it but update accept queue such that node B is considered as a fallback.

In case that first request fails (e.g. node A doesn't provide us with content, content validation fails, etc.) we will query content from random fallback peers (e.g. node B).