Implement configurable requesting of packed chunks from peers

[shizzard]

@JamesPiechota WIP version implemented

[JamesPiechota]

PR looks good! I'd suggest loading the config once during init and storing it in the #state. I'm not sure how significant an impact the get_env call will have (may be minor), but during heavy syncing we might expect this call to happen hundreds of times a second (and billions of times overall) so it may add up

[shizzard]

The actual ar_storage_module:get_packing(StoreID) is O(n) as it traverses the list. Is this will become a problem, this is potential candidate for optimization.

[JamesPiechota]

LGTM!

[shizzard]

The way to configure the distributed packing.
Vocabulary:

• miner node: the node collecting the packed chunks;
• packer node: the node packing chunks for the miner node.

Miner node must have the following configuration options:

• local_peer <packer-node-host>:<packer-node-port>: should be added for each packer node available;
• sync_from_local_peers_only: only allows miner node to sync chunks only from the list of local peers;
• data_sync_request_packed_chunks: forces requesting the already packed chunks.

Packer node must have the following configuration options:

• enable pack_served_chunks: enables packer node to pack the requested chunks with the address and composite depth requested by the peer.

After starting the packer nodes with the option described above, reconfigure the miner node.
You can verify the actual requested packing by sniffing the traffic on the pacler node, looking for the GET /chunk2/<chink-id> requests and the x-packing header:

GET /chunk2/4566605654 HTTP/1.1
host: 127.0.0.1:1985
X-Block-Format: 3
X-Network: arweave.N.1
X-Version: 8
x-bucket-based-offset: true
x-p2p-port: 1995
x-packing: composite_P6SbdirPgsRBnSz8SBMQd5R1kQaZDoLbwisb9I1wqzk.2  <--
x-release: 72