## 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.
