Shift networking configuration into configs

[AgeManning]

Description

The following consensus PRs shift some of the network constants into the configuration files:

• Moved configuration into network preset instead of constants. ethereum/consensus-specs#3394
• Add networking configs to config files ethereum/consensus-specs#3375

We should move these constants also.

Our configuration setup is located here: https://github.com/sigp/lighthouse/blob/stable/consensus/types/src/eth_spec.rs

We need to modify this to incorporate constants and in the associated code. Please hit me up for further info/help if needed :)

[AgeManning]

The configurations we need to add are:

name	default value	location in code to replace
gossip_max_size	10485760	here EDIT: We use the 10x version as the default and divide by 10 for the pre-merge version.
max_request_blocks	1024	here
epochs_per_subnet_subscription	256 - I think this is already there	N/A
min_epochs_for_block_requests	33024	I dont think we have this, but it should go in this function and the blocks_by_root. @pawanjay176 can help here
max_chunk_size	1048576	here
ttfb_timeout	5	here
resp_timeout	10	here
attestation_propagation_slot_range	32	This is currently not configureable, but we can add it here - check with @michaelsproul
maximum_gossip_clock_disparity	500	here @michaelsproul might be able to help with this one
message_domain_invalid_snappy	0x00000000	we don't use it, but it's here
message_domain_valid_snappy	0x01000000	here
subnets_per_node	2 - already there I think	N/A

So what we need to do, is add these fields into the ChainSpec: https://github.com/sigp/lighthouse/blob/stable/consensus/types/src/chain_spec.rs#L32

We should add them into the networking section here: https://github.com/sigp/lighthouse/blob/stable/consensus/types/src/chain_spec.rs#L165

Then for each of the hard-coded networks, i.e mainnet, put in the default values: https://github.com/sigp/lighthouse/blob/stable/consensus/types/src/chain_spec.rs#L473

For all the networks, just use the defaults listed above.

Then for all the places where we have these values being used in the code, replace them with the values from the chain spec.

Most places should have access to a generic EthSpec type. You can get ChainSpec values via: EthSpec::default_spec().

So for example, the first one is gossip_max_size. The location for that variable is here. We should remove that constant (and the one underneath it, as its just 10x the value.

Then in the code that we are using it, like here: https://github.com/sigp/lighthouse/blob/stable/beacon_node/lighthouse_network/src/config.rs#L47 and here: https://github.com/sigp/lighthouse/blob/stable/beacon_node/lighthouse_network/src/config.rs#L457 we need to accept an EthSpec.

So, ideally the function could require the generic, i.e

pub fn gossipsub_config<TSpec:EthSpec>(...) { ... }

It gets used here: so you can pass the TSpec into the function.

That should resolve the first one.

@pawanjay176 should be able to help with all of these.