Shift networking configuration (#4426)

## Issue Addressed
Addresses [#4401](https://github.com/sigp/lighthouse/issues/4401)

## Proposed Changes
Shift some constants into ```ChainSpec``` and remove the constant values from code space.

## Additional Info

I mostly used ```MainnetEthSpec::default_spec()``` for getting ```ChainSpec```. I wonder Did I make a mistake about that.


Co-authored-by: armaganyildirak <armaganyildirak@gmail.com>
Co-authored-by: Paul Hauner <paul@paulhauner.com>
Co-authored-by: Age Manning <Age@AgeManning.com>
Co-authored-by: Diva M <divma@protonmail.com>

beacon_node/http_api/src/sync_committees.rs

@@ -6,7 +6,7 @@ use beacon_chain::sync_committee_verification::{
 };
 use beacon_chain::{
     validator_monitor::timestamp_now, BeaconChain, BeaconChainError, BeaconChainTypes,
-    StateSkipConfig, MAXIMUM_GOSSIP_CLOCK_DISPARITY,
+    StateSkipConfig,
 };
 use eth2::types::{self as api_types};
 use lighthouse_network::PubsubMessage;
@@ -85,7 +85,7 @@ fn duties_from_state_load<T: BeaconChainTypes>(
     let current_epoch = chain.epoch()?;
     let tolerant_current_epoch = chain
         .slot_clock
-        .now_with_future_tolerance(MAXIMUM_GOSSIP_CLOCK_DISPARITY)
+        .now_with_future_tolerance(chain.spec.maximum_gossip_clock_disparity())
         .ok_or(BeaconChainError::UnableToReadSlot)?
         .epoch(T::EthSpec::slots_per_epoch());