Add API to compute discrete validator attestation performance (#2874)

## Issue Addressed

N/A

## Proposed Changes

Add a HTTP API which can be used to compute the attestation performances of a validator (or all validators) over a discrete range of epochs.
Performances can be computed for a single validator, or for the global validator set. 

## Usage
### Request
The API can be used as follows:
```
curl "http://localhost:5052/lighthouse/analysis/attestation_performance/{validator_index}?start_epoch=57730&end_epoch=57732"
```
Alternatively, to compute performances for the global validator set:
```
curl "http://localhost:5052/lighthouse/analysis/attestation_performance/global?start_epoch=57730&end_epoch=57732"
```

### Response
The response is JSON formatted as follows:
```
[
  {
    "index": 72,
    "epochs": {
      "57730": {
        "active": true,
        "head": false,
        "target": false,
        "source": false
      },
      "57731": {
        "active": true,
        "head": true,
        "target": true,
        "source": true,
        "delay": 1
      },
      "57732": {
        "active": true,
        "head": true,
        "target": true,
        "source": true,
        "delay": 1
      },
    }
  }
]
```
> Note that the `"epochs"` are not guaranteed to be in ascending order. 

## Additional Info

- This API is intended to be used in our upcoming validator analysis tooling (#2873) and will likely not be very useful for regular users. Some advanced users or block explorers may find this API useful however.
- The request range is limited to 100 epochs (since the range is inclusive and it also computes the `end_epoch` it's actually 101 epochs) to prevent Lighthouse using exceptionally large amounts of memory.

beacon_node/http_api/src/lib.rs

@@ -5,6 +5,7 @@
 //! There are also some additional, non-standard endpoints behind the `/lighthouse/` path which are
 //! used for development.
 
+mod attestation_performance;
 mod attester_duties;
 mod block_id;
 mod block_rewards;
@@ -2541,7 +2542,9 @@ pub fn serve<T: BeaconChainTypes>(
             },
         );
 
+    // GET lighthouse/analysis/block_rewards
     let get_lighthouse_block_rewards = warp::path("lighthouse")
+        .and(warp::path("analysis"))
         .and(warp::path("block_rewards"))
         .and(warp::query::<eth2::lighthouse::BlockRewardsQuery>())
         .and(warp::path::end())
@@ -2551,6 +2554,20 @@ pub fn serve<T: BeaconChainTypes>(
             blocking_json_task(move || block_rewards::get_block_rewards(query, chain, log))
         });
 
+    // GET lighthouse/analysis/attestation_performance/{index}
+    let get_lighthouse_attestation_performance = warp::path("lighthouse")
+        .and(warp::path("analysis"))
+        .and(warp::path("attestation_performance"))
+        .and(warp::path::param::<String>())
+        .and(warp::query::<eth2::lighthouse::AttestationPerformanceQuery>())
+        .and(warp::path::end())
+        .and(chain_filter.clone())
+        .and_then(|target, query, chain: Arc<BeaconChain<T>>| {
+            blocking_json_task(move || {
+                attestation_performance::get_attestation_performance(target, query, chain)
+            })
+        });
+
     let get_events = eth1_v1
         .and(warp::path("events"))
         .and(warp::path::end())
@@ -2676,6 +2693,7 @@ pub fn serve<T: BeaconChainTypes>(
                 .or(get_lighthouse_staking.boxed())
                 .or(get_lighthouse_database_info.boxed())
                 .or(get_lighthouse_block_rewards.boxed())
+                .or(get_lighthouse_attestation_performance.boxed())
                 .or(get_events.boxed()),
         )
         .or(warp::post().and(